Use .toLowerCase and .toUpperCase(Locale.ROOT) (#10182)

* Use .toLowerCase and .toUpperCase(Locale.ROOT)

* Spaces

* add spaces after if(

106 files changed, 444 insertions, 309 deletions

diff --git a/client/src/main/java/com/vaadin/client/CSSRule.java b/client/src/main/java/com/vaadin/client/CSSRule.java
index b351d9c36b..c425fbd2ce 100644
--- a/client/src/main/java/com/vaadin/client/CSSRule.java
+++ b/client/src/main/java/com/vaadin/client/CSSRule.java
@@ -64,7 +64,7 @@ public class CSSRule {
     if (!$doc.styleSheets)
     return null;
     
-    selector = selector.toLowerCase();
+    selector = selector.toLowerCase('en');
     
     var allMatches = [];
     
@@ -87,7 +87,7 @@ public class CSSRule {
     for (var i=0; i<j; i++) {
         var r = theRules[i];
         if (r.type == 1 || sheet.imports) {
-            var selectors = r.selectorText.toLowerCase().split(",");
+            var selectors = r.selectorText.toLowerCase('en').split(",");
             var n = selectors.length;
             for (var m=0; m<n; m++) {
                 if (selectors[m].replace(/^\s+|\s+$/g, "") == selector) {
diff --git a/client/src/main/java/com/vaadin/client/ComputedStyle.java b/client/src/main/java/com/vaadin/client/ComputedStyle.java
index 7d2b3fb732..b54ee64ed4 100644
--- a/client/src/main/java/com/vaadin/client/ComputedStyle.java
+++ b/client/src/main/java/com/vaadin/client/ComputedStyle.java
@@ -83,7 +83,7 @@ public class ComputedStyle {
         if (cs.getPropertyValue) {
 
             // Convert name to dashed format
-            name = name.replace(/([A-Z])/g, "-$1").toLowerCase();
+            name = name.replace(/([A-Z])/g, "-$1").toLowerCase('en');
             var ret = cs.getPropertyValue(name);
 
         } else {
diff --git a/client/src/main/java/com/vaadin/client/WidgetUtil.java b/client/src/main/java/com/vaadin/client/WidgetUtil.java
index 7d54ac7650..94439dc945 100644
--- a/client/src/main/java/com/vaadin/client/WidgetUtil.java
+++ b/client/src/main/java/com/vaadin/client/WidgetUtil.java
@@ -18,6 +18,7 @@ package com.vaadin.client;
 
 import java.io.Serializable;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Logger;
 
@@ -1888,7 +1889,7 @@ public class WidgetUtil {
                 ErrorLevel errorLevel) {
             for (ErrorLevel errorLevelValue : ErrorLevel.values()) {
                 String className = prefix + "-"
-                        + errorLevelValue.toString().toLowerCase();
+                        + errorLevelValue.toString().toLowerCase(Locale.ROOT);
                 if (errorLevel == errorLevelValue) {
                     element.addClassName(className);
                 } else {
diff --git a/client/src/main/java/com/vaadin/client/debug/internal/SelectorPath.java b/client/src/main/java/com/vaadin/client/debug/internal/SelectorPath.java
index 07da3fbd4a..19a1682f49 100644
--- a/client/src/main/java/com/vaadin/client/debug/internal/SelectorPath.java
+++ b/client/src/main/java/com/vaadin/client/debug/internal/SelectorPath.java
@@ -18,6 +18,7 @@ package com.vaadin.client.debug.internal;
 
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import com.google.gwt.dom.client.Element;
@@ -199,7 +200,7 @@ public class SelectorPath {
         name = getNameWithCount(name);
 
         // Use direct path and elementX naming style.
-        return "WebElement " + name.substring(0, 1).toLowerCase()
+        return "WebElement " + name.substring(0, 1).toLowerCase(Locale.ROOT)
                 + name.substring(1) + " = getDriver().findElement(By.vaadin(\""
                 + path + "\"));";
     }
@@ -242,7 +243,8 @@ public class SelectorPath {
         name = name.replaceAll("\\W", "");
 
         // Lowercase the first character of name
-        return elementType + "Element " + name.substring(0, 1).toLowerCase()
+        return elementType + "Element "
+                + name.substring(0, 1).toLowerCase(Locale.ROOT)
                 + name.substring(1) + " = ";
     }
 
diff --git a/client/src/main/java/com/vaadin/client/event/PointerEventSupportImpl.java b/client/src/main/java/com/vaadin/client/event/PointerEventSupportImpl.java
index 9ceeb86994..3fa3ecd6eb 100644
--- a/client/src/main/java/com/vaadin/client/event/PointerEventSupportImpl.java
+++ b/client/src/main/java/com/vaadin/client/event/PointerEventSupportImpl.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.client.event;
 
+import java.util.Locale;
+
 import com.vaadin.client.event.PointerEvent.EventType;
 
 /**
@@ -38,7 +40,7 @@ public class PointerEventSupportImpl {
      * @return the native event name of the given event
      */
     public String getNativeEventName(EventType eventName) {
-        return eventName.toString().toLowerCase();
+        return eventName.toString().toLowerCase(Locale.ROOT);
     }
 
     /**
diff --git a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
index cb2870cf7a..52b9d1f0ea 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DragSourceExtensionConnector.java
@@ -16,6 +16,7 @@
 package com.vaadin.client.extensions;
 
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Logger;
 
@@ -490,7 +491,7 @@ public class DragSourceExtensionConnector extends AbstractExtensionConnector {
             assert dropEffect != null : "Drop effect should never be null";
 
             sendDragEndEventToServer(nativeEvent,
-                    DropEffect.valueOf(dropEffect.toUpperCase()));
+                    DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)));
         }
     }
 
diff --git a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
index 3791db53b4..b9ce983dab 100644
--- a/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
+++ b/client/src/main/java/com/vaadin/client/extensions/DropTargetExtensionConnector.java
@@ -19,6 +19,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
@@ -219,7 +220,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
             DataTransfer.DropEffect dropEffect = DataTransfer.DropEffect
                     // the valueOf() needs to have equal string and name()
                     // doesn't return in all upper case
-                    .valueOf(getState().dropEffect.name().toUpperCase());
+                    .valueOf(getState().dropEffect.name()
+                            .toUpperCase(Locale.ROOT));
             event.getDataTransfer().setDropEffect(dropEffect);
         }
     }
@@ -283,13 +285,13 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
             JsArrayString typesJsArray = getTypes(
                     nativeEvent.getDataTransfer());
 
-            /* Handle event if transfer doesn't contain files.
+            /*
+             * Handle event if transfer doesn't contain files.
              *
              * Spec: "Dragging files can currently only happen from outside a
              * browsing context, for example from a file system manager
-             * application."
-             * Thus there cannot be at the same time both files and other data
-             * dragged
+             * application." Thus there cannot be at the same time both files
+             * and other data dragged
              */
             if (!containsFiles(typesJsArray)) {
                 nativeEvent.preventDefault();
@@ -304,7 +306,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
                 }
 
                 sendDropEventToServer(types, data, DragSourceExtensionConnector
-                        .getDropEffect(nativeEvent.getDataTransfer()), nativeEvent);
+                        .getDropEffect(nativeEvent.getDataTransfer()),
+                        nativeEvent);
             }
 
         }
@@ -332,8 +335,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
         }
 
         // Execute criterion defined via API
-        if (allowed && getState().criteria != null && !getState().criteria
-                .isEmpty()) {
+        if (allowed && getState().criteria != null
+                && !getState().criteria.isEmpty()) {
 
             // Collect payload data types
             Set<Payload> payloadSet = new HashSet<>();
@@ -370,7 +373,7 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
      * https://html.spec.whatwg.org/multipage/interaction.html#the-datatransfer-interface:dom-datatransfer-types-2
      *
      * @param types
-     *         Array of data types.
+     *            Array of data types.
      * @return {@code} true if given array contains {@code "Files"}, {@code
      * false} otherwise.
      */
@@ -403,8 +406,8 @@ public class DropTargetExtensionConnector extends AbstractExtensionConnector {
                 .buildMouseEventDetails(dropEvent, getDropTargetElement());
 
         // Send data to server with RPC
-        getRpcProxy(DropTargetRpc.class)
-                .drop(types, data, dropEffect, mouseEventDetails);
+        getRpcProxy(DropTargetRpc.class).drop(types, data, dropEffect,
+                mouseEventDetails);
     }
 
     /**
diff --git a/client/src/main/java/com/vaadin/client/ui/VComboBox.java b/client/src/main/java/com/vaadin/client/ui/VComboBox.java
index 683f04a942..df134c4505 100644
--- a/client/src/main/java/com/vaadin/client/ui/VComboBox.java
+++ b/client/src/main/java/com/vaadin/client/ui/VComboBox.java
@@ -21,6 +21,7 @@ import java.util.Collection;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 import com.google.gwt.animation.client.AnimationScheduler;
@@ -1164,8 +1165,9 @@ public class VComboBox extends Composite implements Field, KeyDownHandler,
                     // TODO try to select the new value if it matches what was
                     // sent for V7 compatibility
                 }
-            } else if (item != null && !"".equals(lastFilter) && item.getText()
-                    .toLowerCase().contains(lastFilter.toLowerCase())) {
+            } else if (item != null && !"".equals(lastFilter)
+                    && item.getText().toLowerCase(Locale.ROOT)
+                            .contains(lastFilter.toLowerCase(Locale.ROOT))) {
                 doItemAction(item, true);
             } else {
                 // currentSuggestion has key="" for nullselection
diff --git a/client/src/main/java/com/vaadin/client/ui/VContextMenu.java b/client/src/main/java/com/vaadin/client/ui/VContextMenu.java
index 7d2f718566..e6aabd1af1 100644
--- a/client/src/main/java/com/vaadin/client/ui/VContextMenu.java
+++ b/client/src/main/java/com/vaadin/client/ui/VContextMenu.java
@@ -16,6 +16,8 @@
 
 package com.vaadin.client.ui;
 
+import java.util.Locale;
+
 import com.google.gwt.core.client.Scheduler;
 import com.google.gwt.dom.client.Element;
 import com.google.gwt.dom.client.NodeList;
@@ -287,7 +289,8 @@ public class VContextMenu extends VOverlay implements SubPartAware {
             com.google.gwt.user.client.Element subElement) {
         if (getElement().isOrHasChild(subElement)) {
             com.google.gwt.dom.client.Element e = subElement;
-            while (e != null && !e.getTagName().toLowerCase().equals("tr")) {
+            while (e != null
+                    && !e.getTagName().toLowerCase(Locale.ROOT).equals("tr")) {
                 e = e.getParentElement();
                 // ApplicationConnection.getConsole().log("Found row");
             }
diff --git a/client/src/main/java/com/vaadin/client/ui/VCustomLayout.java b/client/src/main/java/com/vaadin/client/ui/VCustomLayout.java
index a3e7217685..d66db480ae 100644
--- a/client/src/main/java/com/vaadin/client/ui/VCustomLayout.java
+++ b/client/src/main/java/com/vaadin/client/ui/VCustomLayout.java
@@ -17,6 +17,7 @@
 package com.vaadin.client.ui;
 
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.google.gwt.dom.client.Element;
@@ -271,7 +272,7 @@ public class VCustomLayout extends ComplexPanel {
         scripts = "";
         int endOfPrevScript = 0;
         int nextPosToCheck = 0;
-        String lc = html.toLowerCase();
+        String lc = html.toLowerCase(Locale.ROOT);
         String res = "";
         int scriptStart = lc.indexOf("<script", nextPosToCheck);
         while (scriptStart > 0) {
@@ -286,7 +287,7 @@ public class VCustomLayout extends ComplexPanel {
 
         // Extract body
         html = res;
-        lc = html.toLowerCase();
+        lc = html.toLowerCase(Locale.ROOT);
         int startOfBody = lc.indexOf("<body");
         if (startOfBody < 0) {
             res = html;
diff --git a/client/src/main/java/com/vaadin/client/ui/VDateField.java b/client/src/main/java/com/vaadin/client/ui/VDateField.java
index 558ddaa494..971248cee9 100644
--- a/client/src/main/java/com/vaadin/client/ui/VDateField.java
+++ b/client/src/main/java/com/vaadin/client/ui/VDateField.java
@@ -265,7 +265,7 @@ public abstract class VDateField<R extends Enum<R>> extends FlowPanel
      * @return the resolution variable name
      */
     public String getResolutionVariable(R resolution) {
-        return resolution.name().toLowerCase(Locale.ENGLISH);
+        return resolution.name().toLowerCase(Locale.ROOT);
     }
 
     /**
diff --git a/client/src/main/java/com/vaadin/client/ui/VDragAndDropWrapper.java b/client/src/main/java/com/vaadin/client/ui/VDragAndDropWrapper.java
index 0202cdf430..0ef910ac96 100644
--- a/client/src/main/java/com/vaadin/client/ui/VDragAndDropWrapper.java
+++ b/client/src/main/java/com/vaadin/client/ui/VDragAndDropWrapper.java
@@ -17,6 +17,7 @@ package com.vaadin.client.ui;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import com.google.gwt.core.client.GWT;
@@ -672,11 +673,11 @@ public class VDragAndDropWrapper extends VCustomComponent
     protected void deEmphasis(boolean doLayout) {
         if (emphasizedVDrop != null) {
             VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE, false);
-            VDragAndDropWrapper.setStyleName(getElement(),
-                    OVER_STYLE + "-" + emphasizedVDrop.toString().toLowerCase(),
+            VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE + "-"
+                    + emphasizedVDrop.toString().toLowerCase(Locale.ROOT),
                     false);
-            VDragAndDropWrapper.setStyleName(getElement(),
-                    OVER_STYLE + "-" + emphasizedHDrop.toString().toLowerCase(),
+            VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE + "-"
+                    + emphasizedHDrop.toString().toLowerCase(Locale.ROOT),
                     false);
         }
         if (doLayout) {
@@ -692,10 +693,10 @@ public class VDragAndDropWrapper extends VCustomComponent
         deEmphasis(false);
         VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE, true);
         VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE + "-"
-                + verticalDropLocation.toString().toLowerCase(), true);
-        VDragAndDropWrapper.setStyleName(getElement(),
-                OVER_STYLE + "-"
-                        + horizontalDropLocation.toString().toLowerCase(),
+                + verticalDropLocation.toString().toLowerCase(Locale.ROOT),
+                true);
+        VDragAndDropWrapper.setStyleName(getElement(), OVER_STYLE + "-"
+                + horizontalDropLocation.toString().toLowerCase(Locale.ROOT),
                 true);
         emphasizedVDrop = verticalDropLocation;
         emphasizedHDrop = horizontalDropLocation;
diff --git a/client/src/main/java/com/vaadin/client/ui/dd/DragAndDropHandler.java b/client/src/main/java/com/vaadin/client/ui/dd/DragAndDropHandler.java
index 602e692a6e..55e17c325f 100644
--- a/client/src/main/java/com/vaadin/client/ui/dd/DragAndDropHandler.java
+++ b/client/src/main/java/com/vaadin/client/ui/dd/DragAndDropHandler.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.client.ui.dd;
 
+import java.util.Locale;
+
 import com.google.gwt.dom.client.NativeEvent;
 import com.google.gwt.event.dom.client.KeyCodes;
 import com.google.gwt.event.shared.HandlerRegistration;
@@ -174,7 +176,7 @@ public class DragAndDropHandler {
                     public void onPreviewNativeEvent(NativePreviewEvent event) {
                         final int typeInt = event.getTypeInt();
                         if (typeInt == -1 && event.getNativeEvent().getType()
-                                .toLowerCase().contains("pointer")) {
+                                .toLowerCase(Locale.ROOT).contains("pointer")) {
                             /*
                              * Ignore PointerEvents since IE10 and IE11 send
                              * also MouseEvents for backwards compatibility.
diff --git a/client/src/main/java/com/vaadin/client/ui/dd/VDragAndDropManager.java b/client/src/main/java/com/vaadin/client/ui/dd/VDragAndDropManager.java
index f1b2e3736a..4030778d34 100644
--- a/client/src/main/java/com/vaadin/client/ui/dd/VDragAndDropManager.java
+++ b/client/src/main/java/com/vaadin/client/ui/dd/VDragAndDropManager.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.client.ui.dd;
 
+import java.util.Locale;
+
 import com.google.gwt.core.client.GWT;
 import com.google.gwt.core.client.Scheduler;
 import com.google.gwt.dom.client.Element;
@@ -319,7 +321,7 @@ public class VDragAndDropManager {
                                 NativePreviewEvent event) {
                             int typeInt = event.getTypeInt();
                             if (typeInt == -1 && event.getNativeEvent()
-                                    .getType().toLowerCase()
+                                    .getType().toLowerCase(Locale.ROOT)
                                     .contains("pointer")) {
                                 /*
                                  * Ignore PointerEvents since IE10 and IE11 send
diff --git a/client/src/main/java/com/vaadin/client/ui/dd/VDragEvent.java b/client/src/main/java/com/vaadin/client/ui/dd/VDragEvent.java
index 1c038de772..f603fbc464 100644
--- a/client/src/main/java/com/vaadin/client/ui/dd/VDragEvent.java
+++ b/client/src/main/java/com/vaadin/client/ui/dd/VDragEvent.java
@@ -16,6 +16,7 @@
 package com.vaadin.client.ui.dd;
 
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.google.gwt.dom.client.Document;
@@ -257,7 +258,7 @@ public class VDragEvent {
 
         syncContent(element, cloneNode);
         if (BrowserInfo.get().isIE()) {
-            if (cloneNode.getTagName().toLowerCase().equals("tr")) {
+            if (cloneNode.getTagName().toLowerCase(Locale.ROOT).equals("tr")) {
                 TableElement table = Document.get().createTableElement();
                 TableSectionElement tbody = Document.get().createTBodyElement();
                 table.appendChild(tbody);
diff --git a/client/src/main/java/com/vaadin/client/ui/orderedlayout/Slot.java b/client/src/main/java/com/vaadin/client/ui/orderedlayout/Slot.java
index 2faffeede0..63daaf2bc3 100644
--- a/client/src/main/java/com/vaadin/client/ui/orderedlayout/Slot.java
+++ b/client/src/main/java/com/vaadin/client/ui/orderedlayout/Slot.java
@@ -17,6 +17,7 @@
 package com.vaadin.client.ui.orderedlayout;
 
 import java.util.List;
+import java.util.Locale;
 
 import com.google.gwt.aria.client.Roles;
 import com.google.gwt.core.client.GWT;
@@ -387,8 +388,8 @@ public class Slot extends SimplePanel implements HasErrorIndicatorElement {
         if (caption == null) {
             return;
         }
-        captionWrap.removeClassName(
-                "v-caption-on-" + this.captionPosition.name().toLowerCase());
+        captionWrap.removeClassName("v-caption-on-"
+                + this.captionPosition.name().toLowerCase(Locale.ROOT));
 
         this.captionPosition = captionPosition;
         if (captionPosition == CaptionPosition.BOTTOM
@@ -398,8 +399,8 @@ public class Slot extends SimplePanel implements HasErrorIndicatorElement {
             captionWrap.insertFirst(caption);
         }
 
-        captionWrap.addClassName(
-                "v-caption-on-" + captionPosition.name().toLowerCase());
+        captionWrap.addClassName("v-caption-on-"
+                + captionPosition.name().toLowerCase(Locale.ROOT));
     }
 
     /**
diff --git a/client/src/main/java/com/vaadin/client/ui/orderedlayout/VAbstractOrderedLayout.java b/client/src/main/java/com/vaadin/client/ui/orderedlayout/VAbstractOrderedLayout.java
index 6dcc78feeb..80fbe7a079 100644
--- a/client/src/main/java/com/vaadin/client/ui/orderedlayout/VAbstractOrderedLayout.java
+++ b/client/src/main/java/com/vaadin/client/ui/orderedlayout/VAbstractOrderedLayout.java
@@ -16,6 +16,7 @@
 package com.vaadin.client.ui.orderedlayout;
 
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.google.gwt.core.client.GWT;
@@ -345,8 +346,8 @@ public class VAbstractOrderedLayout extends FlowPanel {
             return CaptionPosition.TOP;
         }
         String captionClass = matcher.getGroup(1);
-        CaptionPosition captionPosition = CaptionPosition
-                .valueOf(CaptionPosition.class, captionClass.toUpperCase());
+        CaptionPosition captionPosition = CaptionPosition.valueOf(
+                CaptionPosition.class, captionClass.toUpperCase(Locale.ROOT));
         return captionPosition;
     }
 
diff --git a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VFilterSelect.java b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VFilterSelect.java
index bbbf33f5a4..0d1830e829 100644
--- a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VFilterSelect.java
+++ b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VFilterSelect.java
@@ -21,6 +21,7 @@ import java.util.Collection;
 import java.util.Date;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 import com.google.gwt.aria.client.Roles;
@@ -934,7 +935,7 @@ public class VFilterSelect extends Composite
         private void setTdWidth(Node parent, int width) {
             for (int i = 0; i < parent.getChildCount(); i++) {
                 Node child = parent.getChild(i);
-                if ("td".equals(child.getNodeName().toLowerCase())) {
+                if ("td".equals(child.getNodeName().toLowerCase(Locale.ROOT))) {
                     ((Element) child).getStyle().setWidth(width, Unit.PX);
                 } else {
                     setTdWidth(child, width);
@@ -1204,10 +1205,11 @@ public class VFilterSelect extends Composite
                 }
             } else if (item != null && !"".equals(lastFilter)
                     && (filteringmode == FilteringMode.CONTAINS
-                            ? item.getText().toLowerCase()
-                                    .contains(lastFilter.toLowerCase())
-                            : item.getText().toLowerCase()
-                                    .startsWith(lastFilter.toLowerCase()))) {
+                            ? item.getText().toLowerCase(Locale.ROOT).contains(
+                                    lastFilter.toLowerCase(Locale.ROOT))
+                            : item.getText().toLowerCase(Locale.ROOT)
+                                    .startsWith(lastFilter
+                                            .toLowerCase(Locale.ROOT)))) {
                 doItemAction(item, true);
             } else {
                 // currentSuggestion has key="" for nullselection
diff --git a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VScrollTable.java b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VScrollTable.java
index af255c4e5b..16817fd82d 100644
--- a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VScrollTable.java
+++ b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/VScrollTable.java
@@ -23,6 +23,7 @@ import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.logging.Level;
@@ -5904,8 +5905,8 @@ public class VScrollTable extends FlowPanel
 
                 TooltipInfo info = null;
                 final Element targetTdOrTr = getTdOrTr(target);
-                if (targetTdOrTr != null && "td"
-                        .equals(targetTdOrTr.getTagName().toLowerCase())) {
+                if (targetTdOrTr != null && "td".equals(
+                        targetTdOrTr.getTagName().toLowerCase(Locale.ROOT))) {
                     TableCellElement td = (TableCellElement) targetTdOrTr
                             .cast();
                     info = cellToolTips.get(td);
@@ -7593,7 +7594,7 @@ public class VScrollTable extends FlowPanel
                         && row.rowKey == lastEmphasized.overkey) {
                     String stylename = ROWSTYLEBASE
                             + lastEmphasized.dropLocation.toString()
-                                    .toLowerCase();
+                                    .toLowerCase(Locale.ROOT);
                     VScrollTableRow.setStyleName(row.getElement(), stylename,
                             false);
                     lastEmphasized = null;
@@ -7614,8 +7615,8 @@ public class VScrollTable extends FlowPanel
             for (Widget w : scrollBody.renderedRows) {
                 VScrollTableRow row = (VScrollTableRow) w;
                 if (details != null && details.overkey == row.rowKey) {
-                    String stylename = ROWSTYLEBASE
-                            + details.dropLocation.toString().toLowerCase();
+                    String stylename = ROWSTYLEBASE + details.dropLocation
+                            .toString().toLowerCase(Locale.ROOT);
                     VScrollTableRow.setStyleName(row.getElement(), stylename,
                             true);
                     lastEmphasized = details;
diff --git a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/combobox/ComboBoxConnector.java b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/combobox/ComboBoxConnector.java
index b3b4405a1b..e064eb9dad 100644
--- a/compatibility-client/src/main/java/com/vaadin/v7/client/ui/combobox/ComboBoxConnector.java
+++ b/compatibility-client/src/main/java/com/vaadin/v7/client/ui/combobox/ComboBoxConnector.java
@@ -17,6 +17,7 @@ package com.vaadin.v7.client.ui.combobox;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 
 import com.google.gwt.core.client.Scheduler;
 import com.google.gwt.core.client.Scheduler.ScheduledCommand;
@@ -202,8 +203,9 @@ public class ComboBoxConnector extends AbstractFieldConnector
             }
         }
 
-        if ((getWidget().waitingForFilteringResponse && getWidget().lastFilter
-                .toLowerCase().equals(uidl.getStringVariable("filter")))
+        if ((getWidget().waitingForFilteringResponse
+                && getWidget().lastFilter.toLowerCase(Locale.ROOT)
+                        .equals(uidl.getStringVariable("filter")))
                 || popupOpenAndCleared) {
 
             getWidget().suggestionPopup.showSuggestions(
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/fieldgroup/FieldGroup.java b/compatibility-server/src/main/java/com/vaadin/v7/data/fieldgroup/FieldGroup.java
index 87cc641322..af120108e3 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/fieldgroup/FieldGroup.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/fieldgroup/FieldGroup.java
@@ -23,6 +23,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import com.vaadin.annotations.PropertyId;
@@ -1065,7 +1066,7 @@ public class FieldGroup implements Serializable {
     }
 
     protected static String minifyFieldName(String fieldName) {
-        return fieldName.toLowerCase().replace("_", "");
+        return fieldName.toLowerCase(Locale.ROOT).replace("_", "");
     }
 
     /**
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/Like.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/Like.java
index 3c60f83f78..12d8997ad5 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/Like.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/Like.java
@@ -15,15 +15,19 @@
  */
 package com.vaadin.v7.data.util.filter;
 
+import java.util.Locale;
+
 import com.vaadin.data.provider.DataProvider;
 import com.vaadin.data.provider.ListDataProvider;
 import com.vaadin.v7.data.Container.Filter;
 import com.vaadin.v7.data.Item;
 
 /**
- * @deprecated As of 8.0, the whole filtering feature is integrated into {@link DataProvider}.
- * For in-memory case ({@link ListDataProvider}), use predicates as filters. For back-end DataProviders,
- * filters are specific to the implementation.
+ * @deprecated As of 8.0, the whole filtering feature is integrated into
+ *             {@link DataProvider}. For in-memory case
+ *             ({@link ListDataProvider}), use predicates as filters. For
+ *             back-end DataProviders, filters are specific to the
+ *             implementation.
  */
 @Deprecated
 public class Like implements Filter {
@@ -77,7 +81,8 @@ public class Like implements Filter {
         if (isCaseSensitive()) {
             return colValue.matches(pattern);
         }
-        return colValue.toUpperCase().matches(pattern.toUpperCase());
+        return colValue.toUpperCase(Locale.ROOT)
+                .matches(pattern.toUpperCase(Locale.ROOT));
     }
 
     @Override
@@ -107,7 +112,8 @@ public class Like implements Filter {
                 ? getPropertyId().equals(o.getPropertyId())
                 : null == o.getPropertyId();
         boolean valueEqual = (null != getValue())
-                ? getValue().equals(o.getValue()) : null == o.getValue();
+                ? getValue().equals(o.getValue())
+                : null == o.getValue();
         return propertyIdEqual && valueEqual;
     }
 }
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/SimpleStringFilter.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/SimpleStringFilter.java
index 025437659e..6969b12003 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/SimpleStringFilter.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/filter/SimpleStringFilter.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.v7.data.util.filter;
 
+import java.util.Locale;
+
 import com.vaadin.data.provider.DataProvider;
 import com.vaadin.data.provider.ListDataProvider;
 import com.vaadin.v7.data.Container.Filter;
@@ -37,9 +39,11 @@ import com.vaadin.v7.data.Property;
  *
  * @since 6.6
  *
- * @deprecated As of 8.0, the whole filtering feature is integrated into {@link DataProvider}.
- * For in-memory case ({@link ListDataProvider}), use predicates as filters. For back-end DataProviders,
- * filters are specific to the implementation.
+ * @deprecated As of 8.0, the whole filtering feature is integrated into
+ *             {@link DataProvider}. For in-memory case
+ *             ({@link ListDataProvider}), use predicates as filters. For
+ *             back-end DataProviders, filters are specific to the
+ *             implementation.
  */
 @Deprecated
 public final class SimpleStringFilter implements Filter {
@@ -52,7 +56,7 @@ public final class SimpleStringFilter implements Filter {
     public SimpleStringFilter(Object propertyId, String filterString,
             boolean ignoreCase, boolean onlyMatchPrefix) {
         this.propertyId = propertyId;
-        this.filterString = ignoreCase ? filterString.toLowerCase()
+        this.filterString = ignoreCase ? filterString.toLowerCase(Locale.ROOT)
                 : filterString;
         this.ignoreCase = ignoreCase;
         this.onlyMatchPrefix = onlyMatchPrefix;
@@ -68,7 +72,8 @@ public final class SimpleStringFilter implements Filter {
         if (propertyValue == null) {
             return false;
         }
-        final String value = ignoreCase ? propertyValue.toString().toLowerCase()
+        final String value = ignoreCase
+                ? propertyValue.toString().toLowerCase(Locale.ROOT)
                 : propertyValue.toString();
         if (onlyMatchPrefix) {
             if (!value.startsWith(filterString)) {
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/connection/SimpleJDBCConnectionPool.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/connection/SimpleJDBCConnectionPool.java
index 4021ff0100..0d0c8ed53a 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/connection/SimpleJDBCConnectionPool.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/connection/SimpleJDBCConnectionPool.java
@@ -22,6 +22,7 @@ import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 
 /**
@@ -29,7 +30,7 @@ import java.util.Set;
  * the JDBC driver, setting up the connections and ensuring they are still
  * usable upon release.
  *
- *  @deprecated As of 8.0, no replacement available.
+ * @deprecated As of 8.0, no replacement available.
  */
 @SuppressWarnings("serial")
 @Deprecated
@@ -145,7 +146,7 @@ public class SimpleJDBCConnectionPool implements JDBCConnectionPool {
         Connection c = DriverManager.getConnection(connectionUri, userName,
                 password);
         c.setAutoCommit(false);
-        if (driverName.toLowerCase().contains("mysql")) {
+        if (driverName.toLowerCase(Locale.ROOT).contains("mysql")) {
             try {
                 Statement s = c.createStatement();
                 s.execute("SET SESSION sql_mode = 'ANSI'");
@@ -176,8 +177,7 @@ public class SimpleJDBCConnectionPool implements JDBCConnectionPool {
 
     }
 
-    private void writeObject(ObjectOutputStream out)
-            throws IOException {
+    private void writeObject(ObjectOutputStream out) throws IOException {
         initialized = false;
         out.defaultWriteObject();
     }
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/FreeformQuery.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/FreeformQuery.java
index 4575a51904..4e4a0d5f26 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/FreeformQuery.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/FreeformQuery.java
@@ -25,6 +25,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 
 import com.vaadin.v7.data.Container.Filter;
 import com.vaadin.v7.data.util.sqlcontainer.RowItem;
@@ -478,7 +479,7 @@ public class FreeformQuery extends AbstractTransactionalQuery
             }
         }
         // Is there already a WHERE clause in the query string?
-        int index = queryString.toLowerCase().indexOf("where ");
+        int index = queryString.toLowerCase(Locale.ROOT).indexOf("where ");
         if (index > -1) {
             // Rewrite the where clause
             return queryString.substring(0, index) + "WHERE " + where + " AND "
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/TableQuery.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/TableQuery.java
index 8aa6aa0c26..51c87d960f 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/TableQuery.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/TableQuery.java
@@ -28,6 +28,7 @@ import java.util.EventObject;
 import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -559,13 +560,13 @@ public class TableQuery extends AbstractTransactionalQuery
                         null);
                 if (!tables.next()) {
                     String catalog = (catalogName != null)
-                            ? catalogName.toUpperCase()
+                            ? catalogName.toUpperCase(Locale.ROOT)
                             : null;
                     String schema = (schemaName != null)
-                            ? schemaName.toUpperCase()
+                            ? schemaName.toUpperCase(Locale.ROOT)
                             : null;
                     tables = dbmd.getTables(catalog, schema,
-                            tableName.toUpperCase(), null);
+                            tableName.toUpperCase(Locale.ROOT), null);
                     if (!tables.next()) {
                         throw new IllegalArgumentException(
                                 "Table with the name \"" + getFullTableName()
@@ -573,7 +574,7 @@ public class TableQuery extends AbstractTransactionalQuery
                     } else {
                         catalogName = catalog;
                         schemaName = schema;
-                        tableName = tableName.toUpperCase();
+                        tableName = tableName.toUpperCase(Locale.ROOT);
                     }
                 }
                 tables.close();
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/generator/filter/LikeTranslator.java b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/generator/filter/LikeTranslator.java
index 292187beec..bf0de08670 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/generator/filter/LikeTranslator.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/data/util/sqlcontainer/query/generator/filter/LikeTranslator.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.v7.data.util.sqlcontainer.query.generator.filter;
 
+import java.util.Locale;
+
 import com.vaadin.v7.data.Container.Filter;
 import com.vaadin.v7.data.util.filter.Like;
 import com.vaadin.v7.data.util.sqlcontainer.query.generator.StatementHelper;
@@ -37,7 +39,7 @@ public class LikeTranslator implements FilterTranslator {
             sh.addParameterValue(like.getValue());
             return QueryBuilder.quote(like.getPropertyId()) + " LIKE ?";
         } else {
-            sh.addParameterValue(like.getValue().toUpperCase());
+            sh.addParameterValue(like.getValue().toUpperCase(Locale.ROOT));
             return "UPPER(" + QueryBuilder.quote(like.getPropertyId())
                     + ") LIKE ?";
         }
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/ui/AbstractColorPicker.java b/compatibility-server/src/main/java/com/vaadin/v7/ui/AbstractColorPicker.java
index 8fb42de9ed..a3066a1de0 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/ui/AbstractColorPicker.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/ui/AbstractColorPicker.java
@@ -18,6 +18,7 @@ package com.vaadin.v7.ui;
 import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.util.Collection;
+import java.util.Locale;
 
 import org.jsoup.nodes.Attributes;
 import org.jsoup.nodes.Element;
@@ -556,8 +557,8 @@ public abstract class AbstractColorPicker extends AbstractLegacyComponent
             setColor(new Color(Integer.parseInt(hexColor, 16)));
         }
         if (design.hasAttr("popup-style")) {
-            setPopupStyle(PopupStyle.valueOf(
-                    "POPUP_" + attributes.get("popup-style").toUpperCase()));
+            setPopupStyle(PopupStyle.valueOf("POPUP_"
+                    + attributes.get("popup-style").toUpperCase(Locale.ROOT)));
         }
         if (design.hasAttr("position")) {
             String[] position = attributes.get("position").split(",");
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/ui/Calendar.java b/compatibility-server/src/main/java/com/vaadin/v7/ui/Calendar.java
index bd6e0d6902..b7c8feff64 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/ui/Calendar.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/ui/Calendar.java
@@ -1958,8 +1958,8 @@ public class Calendar extends AbstractLegacyComponent
 
         Attributes attr = design.attributes();
         if (design.hasAttr("time-format")) {
-            setTimeFormat(TimeFormat.valueOf(
-                    "Format" + design.attr("time-format").toUpperCase()));
+            setTimeFormat(TimeFormat.valueOf("Format"
+                    + design.attr("time-format").toUpperCase(Locale.ROOT)));
         }
 
         if (design.hasAttr("start-date")) {
diff --git a/compatibility-server/src/main/java/com/vaadin/v7/ui/themes/Runo.java b/compatibility-server/src/main/java/com/vaadin/v7/ui/themes/Runo.java
index 727b44ce37..f603d8c966 100644
--- a/compatibility-server/src/main/java/com/vaadin/v7/ui/themes/Runo.java
+++ b/compatibility-server/src/main/java/com/vaadin/v7/ui/themes/Runo.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.v7.ui.themes;
 
+import java.util.Locale;
+
 import com.vaadin.ui.themes.ValoTheme;
 
 /**
@@ -27,7 +29,7 @@ public class Runo extends BaseTheme {
     public static final String THEME_NAME = "runo";
 
     public static String themeName() {
-        return THEME_NAME.toLowerCase();
+        return THEME_NAME.toLowerCase(Locale.ROOT);
     }
 
     /***************************************************************************
diff --git a/compatibility-server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java b/compatibility-server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
index 0252da62ac..42e7cd4d0c 100644
--- a/compatibility-server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
+++ b/compatibility-server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
@@ -7,6 +7,7 @@ import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 
 import org.easymock.EasyMock;
@@ -43,7 +44,7 @@ public abstract class AbstractListenerMethodsTestBase {
                     String packageName = "com.vaadin.tests.server";
                     if (Component.class.isAssignableFrom(c)) {
                         packageName += ".component."
-                                + c.getSimpleName().toLowerCase();
+                                + c.getSimpleName().toLowerCase(Locale.ROOT);
                         continue;
                     }
 
diff --git a/server/src/main/java/com/vaadin/data/Binder.java b/server/src/main/java/com/vaadin/data/Binder.java
index 828130bd81..d417944f80 100644
--- a/server/src/main/java/com/vaadin/data/Binder.java
+++ b/server/src/main/java/com/vaadin/data/Binder.java
@@ -2585,7 +2585,7 @@ public class Binder<BEAN> implements Serializable {
     }
 
     private String minifyFieldName(String fieldName) {
-        return fieldName.toLowerCase(Locale.ENGLISH).replace("_", "");
+        return fieldName.toLowerCase(Locale.ROOT).replace("_", "");
     }
 
     private <V> void fireValueChangeEvent(ValueChangeEvent<V> event) {
diff --git a/server/src/main/java/com/vaadin/server/BootstrapHandler.java b/server/src/main/java/com/vaadin/server/BootstrapHandler.java
index ff9e816013..bd87f78d67 100644
--- a/server/src/main/java/com/vaadin/server/BootstrapHandler.java
+++ b/server/src/main/java/com/vaadin/server/BootstrapHandler.java
@@ -662,7 +662,7 @@ public abstract class BootstrapHandler extends SynchronizedRequestHandler {
         mainDiv.addClass("v-app");
         mainDiv.addClass(context.getThemeName());
         mainDiv.addClass(context.getUIClass().getSimpleName()
-                .toLowerCase(Locale.ENGLISH));
+                .toLowerCase(Locale.ROOT));
         if (style != null && !style.isEmpty()) {
             mainDiv.attr("style", style);
         }
diff --git a/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java b/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
index 80db458c42..33f80015fb 100644
--- a/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
+++ b/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
@@ -16,6 +16,7 @@
 
 package com.vaadin.server;
 
+import java.util.Locale;
 import java.util.Properties;
 import java.util.logging.Logger;
 
@@ -144,7 +145,8 @@ public class DefaultDeploymentConfiguration
         }
 
         // Try lowercased system properties
-        val = System.getProperty(pkgName + parameterName.toLowerCase());
+        val = System
+                .getProperty(pkgName + parameterName.toLowerCase(Locale.ROOT));
         if (val != null) {
             return val;
         }
@@ -170,7 +172,8 @@ public class DefaultDeploymentConfiguration
 
         // Try lower case application properties for backward compatibility with
         // 3.0.2 and earlier
-        val = initParameters.getProperty(parameterName.toLowerCase());
+        val = initParameters
+                .getProperty(parameterName.toLowerCase(Locale.ROOT));
 
         return val;
     }
@@ -322,7 +325,8 @@ public class DefaultDeploymentConfiguration
                 Constants.SERVLET_PARAMETER_PUSH_MODE,
                 PushMode.DISABLED.toString());
         try {
-            pushMode = Enum.valueOf(PushMode.class, mode.toUpperCase());
+            pushMode = Enum.valueOf(PushMode.class,
+                    mode.toUpperCase(Locale.ROOT));
         } catch (IllegalArgumentException e) {
             getLogger().warning(Constants.WARNING_PUSH_MODE_NOT_RECOGNIZED);
             pushMode = PushMode.DISABLED;
diff --git a/server/src/main/java/com/vaadin/server/JsonCodec.java b/server/src/main/java/com/vaadin/server/JsonCodec.java
index a7f94de468..fc8e858b3b 100644
--- a/server/src/main/java/com/vaadin/server/JsonCodec.java
+++ b/server/src/main/java/com/vaadin/server/JsonCodec.java
@@ -33,6 +33,7 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -729,7 +730,7 @@ public class JsonCodec implements Serializable {
                     throw new RuntimeException("Can't encode "
                             + valueType.getName()
                             + " as it has multiple properties with the name "
-                            + fieldName.toLowerCase()
+                            + fieldName.toLowerCase(Locale.ROOT)
                             + ". This can happen if there are getters and setters for a public field (the framework can't know which to ignore) or if there are properties with only casing distinguishing between the names (e.g. getFoo() and getFOO())");
                 }
 
diff --git a/server/src/main/java/com/vaadin/server/JsonPaintTarget.java b/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
index b643fbb7a9..4cfb389851 100644
--- a/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
+++ b/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
@@ -26,6 +26,7 @@ import java.util.Deque;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.logging.Level;
@@ -289,7 +290,7 @@ public class JsonPaintTarget implements PaintTarget {
                     for (int k = 0; k < 4 - ss.length(); k++) {
                         sb.append('0');
                     }
-                    sb.append(ss.toUpperCase());
+                    sb.append(ss.toUpperCase(Locale.ROOT));
                 } else {
                     sb.append(ch);
                 }
diff --git a/server/src/main/java/com/vaadin/server/VaadinPortlet.java b/server/src/main/java/com/vaadin/server/VaadinPortlet.java
index d4a7d0e62d..c00b6461d9 100644
--- a/server/src/main/java/com/vaadin/server/VaadinPortlet.java
+++ b/server/src/main/java/com/vaadin/server/VaadinPortlet.java
@@ -20,6 +20,7 @@ import java.io.Serializable;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Enumeration;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.logging.Level;
@@ -561,7 +562,8 @@ public class VaadinPortlet extends GenericPortlet
      */
     protected VaadinPortletRequest createVaadinRequest(PortletRequest request) {
         PortalContext portalContext = request.getPortalContext();
-        String portalInfo = portalContext.getPortalInfo().toLowerCase().trim();
+        String portalInfo = portalContext.getPortalInfo()
+                .toLowerCase(Locale.ROOT).trim();
         VaadinPortletService service = getService();
 
         if (portalInfo.contains("gatein")) {
diff --git a/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java b/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
index a313e8c0fe..d1cdf0dd63 100644
--- a/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
+++ b/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
@@ -24,6 +24,7 @@ import java.net.URL;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -101,12 +102,12 @@ public class SASSAddonImportFileCreator {
             // last
             List<String> paths = new ArrayList<>(addonThemes.keySet());
             Collections.sort(paths, (String path1, String path2) -> {
-                if (path1.toLowerCase().endsWith(".css")
-                        && path2.toLowerCase().endsWith(".scss")) {
+                if (path1.toLowerCase(Locale.ROOT).endsWith(".css")
+                        && path2.toLowerCase(Locale.ROOT).endsWith(".scss")) {
                     return -1;
                 }
-                if (path1.toLowerCase().endsWith(".scss")
-                        && path2.toLowerCase().endsWith(".css")) {
+                if (path1.toLowerCase(Locale.ROOT).endsWith(".scss")
+                        && path2.toLowerCase(Locale.ROOT).endsWith(".css")) {
                     return 1;
                 }
                 return 0;
diff --git a/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java b/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
index 608f84782c..80c8fc7874 100644
--- a/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
+++ b/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
@@ -29,6 +29,7 @@ import java.net.URISyntaxException;
 import java.net.URL;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -180,7 +181,7 @@ public class WidgetSetBuilder {
     }
 
     static boolean isWidgetset(String gwtModuleName) {
-        return gwtModuleName.toLowerCase().contains("widgetset");
+        return gwtModuleName.toLowerCase(Locale.ROOT).contains("widgetset");
     }
 
     private static String readFile(File widgetsetFile) throws IOException {
diff --git a/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java b/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
index 608cdd9cfa..74b7e1f2b1 100644
--- a/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
+++ b/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
@@ -17,6 +17,7 @@ package com.vaadin.ui;
 
 import java.io.Serializable;
 import java.util.Collection;
+import java.util.Locale;
 import java.util.Objects;
 
 import org.jsoup.nodes.Attributes;
@@ -492,8 +493,8 @@ public abstract class AbstractColorPicker extends AbstractField<Color> {
             doSetValue(new Color(Integer.parseInt(hexColor, 16)));
         }
         if (design.hasAttr("popup-style")) {
-            setPopupStyle(PopupStyle.valueOf(
-                    "POPUP_" + attributes.get("popup-style").toUpperCase()));
+            setPopupStyle(PopupStyle.valueOf("POPUP_"
+                    + attributes.get("popup-style").toUpperCase(Locale.ROOT)));
         }
         if (design.hasAttr("position")) {
             String[] position = attributes.get("position").split(",");
diff --git a/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
index 342946d5c9..edb1534a05 100644
--- a/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
@@ -16,6 +16,7 @@
 package com.vaadin.ui.components.grid;
 
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.vaadin.shared.Registration;
@@ -156,7 +157,7 @@ public class GridDropTarget<T> extends DropTargetExtension<Grid<T>> {
 
             GridDropEvent<T> event = new GridDropEvent<>(getParent(),
                     dataPreserveOrder,
-                    DropEffect.valueOf(dropEffect.toUpperCase()),
+                    DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                     getUI().getActiveDragSource(), dropTargetRow, dropLocation,
                     mouseEventDetails);
 
diff --git a/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java b/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
index 1d440b5fec..e471f350bc 100644
--- a/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
@@ -16,6 +16,7 @@
 package com.vaadin.ui.components.grid;
 
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.vaadin.shared.Registration;
@@ -30,7 +31,7 @@ import com.vaadin.ui.TreeGrid;
  * counterpart of GridDropTargetExtensionConnector.
  *
  * @param <T>
- *         Type of the TreeGrid bean.
+ *            Type of the TreeGrid bean.
  * @author Vaadin Ltd
  * @since 8.1
  */
@@ -41,22 +42,22 @@ public class TreeGridDropTarget<T> extends GridDropTarget<T> {
      * drop.
      *
      * @param target
-     *         TreeGrid to be extended.
+     *            TreeGrid to be extended.
      * @param dropMode
-     *         Drop mode that describes the allowed drop locations within the
-     *         TreeGrid's row.
+     *            Drop mode that describes the allowed drop locations within the
+     *            TreeGrid's row.
      */
     public TreeGridDropTarget(TreeGrid<T> target, DropMode dropMode) {
         super(target, dropMode);
     }
 
     /**
-     * Attaches drop listener for the current drop target. {@link
-     * TreeGridDropListener#drop(TreeGridDropEvent)} is called when drop event
-     * happens on the client side.
+     * Attaches drop listener for the current drop target.
+     * {@link TreeGridDropListener#drop(TreeGridDropEvent)} is called when drop
+     * event happens on the client side.
      *
      * @param listener
-     *         Listener to handle drop event.
+     *            Listener to handle drop event.
      * @return Handle to be used to remove this listener.
      */
     public Registration addTreeGridDropListener(
@@ -79,7 +80,7 @@ public class TreeGridDropTarget<T> extends GridDropTarget<T> {
 
             TreeGridDropEvent<T> event = new TreeGridDropEvent<>(getParent(),
                     dataPreserveOrder,
-                    DropEffect.valueOf(dropEffect.toUpperCase()),
+                    DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                     getUI().getActiveDragSource(), dropTargetRow, dropLocation,
                     mouseEventDetails, depth, collapsed);
 
diff --git a/server/src/main/java/com/vaadin/ui/declarative/Design.java b/server/src/main/java/com/vaadin/ui/declarative/Design.java
index 61d35297d0..7c65992967 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/Design.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/Design.java
@@ -265,7 +265,7 @@ public class Design implements Serializable {
             String prefix = context.getPackagePrefix(packageName);
             if (prefix == null) {
                 prefix = packageName.replace('.', '_')
-                        .toLowerCase(Locale.ENGLISH);
+                        .toLowerCase(Locale.ROOT);
                 context.addPackagePrefix(prefix, packageName);
             }
             prefix += "-";
diff --git a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
index e8fa278aba..c508b693f8 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
@@ -25,6 +25,7 @@ import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Level;
@@ -330,7 +331,7 @@ public class DesignAttributeHandler implements Serializable {
             if (builder.length() != 0) {
                 builder.append('-');
             }
-            builder.append(word.toLowerCase());
+            builder.append(word.toLowerCase(Locale.ROOT));
         }
         return builder.toString();
     }
@@ -356,13 +357,13 @@ public class DesignAttributeHandler implements Serializable {
             // written in lower case
             if (matcher.group(1).isEmpty()) {
                 matcher.appendReplacement(result,
-                        matched.toLowerCase() + matcher.group(3));
+                        matched.toLowerCase(Locale.ROOT) + matcher.group(3));
                 // otherwise the first character of the group stays uppercase,
                 // while the others are lower case
             } else {
                 matcher.appendReplacement(result,
                         matcher.group(1) + matched.substring(0, 1)
-                                + matched.substring(1).toLowerCase()
+                                + matched.substring(1).toLowerCase(Locale.ROOT)
                                 + matcher.group(3));
             }
             // in both cases the uppercase letter of the next word (or string's
diff --git a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
index 2caecda8f4..f1e7e25329 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
@@ -104,7 +104,7 @@ public class FieldBinder implements Serializable {
     private void resolveFields(Class<?> classWithFields) {
         for (Field memberField : getFields(classWithFields)) {
             if (Component.class.isAssignableFrom(memberField.getType())) {
-                fieldMap.put(memberField.getName().toLowerCase(Locale.ENGLISH),
+                fieldMap.put(memberField.getName().toLowerCase(Locale.ROOT),
                         memberField);
             }
         }
@@ -180,7 +180,7 @@ public class FieldBinder implements Serializable {
                 return false;
             }
             // validate that the field can be found
-            Field field = fieldMap.get(fieldName.toLowerCase(Locale.ENGLISH));
+            Field field = fieldMap.get(fieldName.toLowerCase(Locale.ROOT));
             if (field == null) {
                 getLogger()
                         .fine("No field was found by identifier " + identifier);
diff --git a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
index de7f5ad5b7..1360671d00 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
@@ -53,7 +53,7 @@ public class DesignEnumConverter<T extends Enum>
         }
         try {
             T result = (T) Enum.valueOf(type,
-                    value.toUpperCase(Locale.ENGLISH));
+                    value.toUpperCase(Locale.ROOT));
             return Result.ok(result);
         } catch (Exception e) {
             return Result.error(e.getMessage());
@@ -66,7 +66,7 @@ public class DesignEnumConverter<T extends Enum>
             return null;
         }
 
-        return value.name().toLowerCase(Locale.ENGLISH);
+        return value.name().toLowerCase(Locale.ROOT);
     }
 
 }
diff --git a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
index d3d2b13170..c0fa46469c 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
@@ -63,7 +63,7 @@ public class DesignResourceConverter implements Converter<String, Resource> {
         String protocol = value.split("://")[0];
         try {
             ResourceConverterByProtocol converter = ResourceConverterByProtocol
-                    .valueOf(protocol.toUpperCase(Locale.ENGLISH));
+                    .valueOf(protocol.toUpperCase(Locale.ROOT));
             return Result.ok(converter.parse(value));
         } catch (IllegalArgumentException iae) {
             return Result.error("Unrecognized protocol: " + protocol);
diff --git a/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
index 76c7195f60..5ee7b0e861 100644
--- a/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
@@ -18,6 +18,7 @@ package com.vaadin.ui.dnd;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 
@@ -75,7 +76,7 @@ public class DropTargetExtension<T extends AbstractComponent>
         registerRpc(
                 (DropTargetRpc) (types, data, dropEffect, mouseEventDetails) ->
                 onDrop(types, data,
-                        DropEffect.valueOf(dropEffect.toUpperCase()),
+                        DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                         mouseEventDetails));
     }
 
diff --git a/server/src/main/java/com/vaadin/util/FileTypeResolver.java b/server/src/main/java/com/vaadin/util/FileTypeResolver.java
index 500e8736e7..48d7916967 100644
--- a/server/src/main/java/com/vaadin/util/FileTypeResolver.java
+++ b/server/src/main/java/com/vaadin/util/FileTypeResolver.java
@@ -19,6 +19,7 @@ package com.vaadin.util;
 import java.io.File;
 import java.io.Serializable;
 import java.util.Collections;
+import java.util.Locale;
 import java.util.Map;
 import java.util.StringTokenizer;
 import java.util.concurrent.ConcurrentHashMap;
@@ -270,7 +271,8 @@ public class FileTypeResolver implements Serializable {
             }
 
             // Return type from extension map, if found
-            final String type = EXT_TO_MIME_MAP.get(ext.toLowerCase());
+            final String type = EXT_TO_MIME_MAP
+                    .get(ext.toLowerCase(Locale.ROOT));
             if (type != null) {
                 return type;
             }
@@ -358,7 +360,7 @@ public class FileTypeResolver implements Serializable {
      *            the new mime-type for <code>extension</code>.
      */
     public static void addExtension(String extension, String MIMEType) {
-        EXT_TO_MIME_MAP.put(extension.toLowerCase(), MIMEType);
+        EXT_TO_MIME_MAP.put(extension.toLowerCase(Locale.ROOT), MIMEType);
     }
 
     /**
diff --git a/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java b/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
index 31c48447a6..cde97441aa 100644
--- a/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
+++ b/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
@@ -79,7 +79,7 @@ public class BinderCustomPropertySetTest {
 
         @Override
         public String getCaption() {
-            return name.toUpperCase(Locale.ENGLISH);
+            return name.toUpperCase(Locale.ROOT);
         }
 
     }
diff --git a/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java b/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
index 6b3d85900d..00961487d3 100644
--- a/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
+++ b/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
@@ -69,7 +69,7 @@ public class GridValueProvider {
                 upperCasePerson);
 
         persons.addFilter(col.getValueProvider(),
-                value -> value.toUpperCase(Locale.ENGLISH).equals(value));
+                value -> value.toUpperCase(Locale.ROOT).equals(value));
 
         List<Person> queryPersons = persons.fetch(new Query<>())
                 .collect(Collectors.toList());
diff --git a/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java b/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
index 9f6253067a..de346dd0aa 100644
--- a/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
+++ b/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
@@ -25,6 +25,7 @@ import java.math.BigDecimal;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.TimeZone;
 
 import org.junit.Before;
@@ -290,9 +291,9 @@ public class DesignFormatterTest {
                 formatter.format(new ThemeResource(themePath)));
 
         assertEquals(fontAwesomeUrl, formatter.format(FontAwesome.AMBULANCE));
-        assertEquals(someOtherFontUrl.toLowerCase(),
+        assertEquals(someOtherFontUrl.toLowerCase(Locale.ROOT),
                 formatter.format(new GenericFontIcon("SomeOther", 0xf0f9))
-                        .toLowerCase());
+                        .toLowerCase(Locale.ROOT));
 
         assertEquals(fileSystemPath,
                 formatter.format(new FileResource(new File(fileSystemPath))));
diff --git a/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java b/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
index 738f0be806..bd0dbbc6e0 100644
--- a/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
+++ b/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
@@ -69,7 +69,7 @@ public class ClasspathHelper {
                         .map(path -> getClassFromFile(path,
                                 classesRoot.toPath()))
                         .filter(Objects::nonNull).collect(Collectors.toList());
-            } else if (classesRoot.getName().toLowerCase(Locale.ENGLISH)
+            } else if (classesRoot.getName().toLowerCase(Locale.ROOT)
                     .endsWith(".jar")) {
                 URI uri = URI.create("jar:" + classesRoot.toURI());
                 FileSystem fileSystem;
diff --git a/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java b/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
index 8a31b8cf98..ba2c424a09 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
@@ -7,6 +7,7 @@ import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 
 import org.easymock.EasyMock;
@@ -43,7 +44,7 @@ public abstract class AbstractListenerMethodsTestBase {
                     String packageName = "com.vaadin.tests.server";
                     if (Component.class.isAssignableFrom(c)) {
                         packageName += ".component."
-                                + c.getSimpleName().toLowerCase();
+                                + c.getSimpleName().toLowerCase(Locale.ROOT);
                         continue;
                     }
 
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
index 80040804cd..6f18a424b8 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
@@ -69,7 +69,7 @@ public abstract class AbstractLocalDateFieldDeclarativeTest<T extends AbstractLo
                         + "date-out-of-range-message='%s' resolution='%s' "
                         + "date-format='%s' lenient parse-error-message='%s'/>",
                 getComponentTag(), end, start, dateOutOfRange,
-                resolution.name().toLowerCase(Locale.ENGLISH), dateFormat,
+                resolution.name().toLowerCase(Locale.ROOT), dateFormat,
                 parseErrorMsg);
 
         T component = getComponentClass().newInstance();
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
index a4768c6f24..61fff27072 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
@@ -74,7 +74,7 @@ public abstract class AbstractLocalDateTimeFieldDeclarativeTest<T extends Abstra
                         + "date-format='%s' lenient parse-error-message='%s'/>",
                 getComponentTag(), DATE_FORMATTER.format(end),
                 DATE_FORMATTER.format(start), dateOutOfRange,
-                resolution.name().toLowerCase(Locale.ENGLISH), dateFormat,
+                resolution.name().toLowerCase(Locale.ROOT), dateFormat,
                 parseErrorMsg);
 
         T component = getComponentClass().newInstance();
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
index 7ba3e6aaca..2416620afe 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
@@ -43,7 +43,7 @@ public abstract class AbstractTextFieldDeclarativeTest<T extends AbstractTextFie
                 "<%s maxlength='%d' placeholder='%s' "
                         + "value-change-mode='%s' value-change-timeout='%d'/>",
                 getComponentTag(), maxLength, placeholder,
-                mode.name().toLowerCase(Locale.ENGLISH), timeout);
+                mode.name().toLowerCase(Locale.ROOT), timeout);
 
         T component = getComponentClass().newInstance();
 
diff --git a/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java b/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
index 8ebc620328..a9b23d7af0 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
@@ -74,7 +74,7 @@ public class CustomLayoutTest {
             field = list.get(0);
         } else {
             for (Field fld : list) {
-                if (fld.getName().toLowerCase(Locale.ENGLISH)
+                if (fld.getName().toLowerCase(Locale.ROOT)
                         .startsWith("buffer")) {
                     field = fld;
                     break;
diff --git a/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
index 8d1d6c6955..a4f824d6fa 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
@@ -82,9 +82,9 @@ public class GridDeclarativeTest extends AbstractListingDeclarativeTest<Grid> {
                         + "<th plain-text column-ids='id'>Id</th></tr>"
                         + "</thead></table></%s>",
                 getComponentTag(),
-                heightMode.toString().toLowerCase(Locale.ENGLISH),
+                heightMode.toString().toLowerCase(Locale.ROOT),
                 frozenColumns, heightByRows,
-                SelectionMode.MULTI.toString().toLowerCase(Locale.ENGLISH),
+                SelectionMode.MULTI.toString().toLowerCase(Locale.ROOT),
                 getComponentTag());
 
         testRead(design, grid);
diff --git a/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
index e7cab55f94..6cac635c6a 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
@@ -61,7 +61,7 @@ public class RichTextAreaDeclarativeTest
         int timeout = 67;
         String design = String.format(
                 "<%s value-change-mode='%s' value-change-timeout='%d'/>",
-                getComponentTag(), mode.name().toLowerCase(Locale.ENGLISH),
+                getComponentTag(), mode.name().toLowerCase(Locale.ROOT),
                 timeout);
 
         RichTextArea component = new RichTextArea();
diff --git a/shared/src/main/java/com/vaadin/shared/VBrowserDetails.java b/shared/src/main/java/com/vaadin/shared/VBrowserDetails.java
index 61161ea3cc..e226751b64 100644
--- a/shared/src/main/java/com/vaadin/shared/VBrowserDetails.java
+++ b/shared/src/main/java/com/vaadin/shared/VBrowserDetails.java
@@ -16,6 +16,7 @@
 package com.vaadin.shared;
 
 import java.io.Serializable;
+import java.util.Locale;
 
 /**
  * Class that parses the user agent string from the browser and provides
@@ -69,7 +70,7 @@ public class VBrowserDetails implements Serializable {
      *            User agent as provided by the browser.
      */
     public VBrowserDetails(String userAgent) {
-        userAgent = userAgent.toLowerCase();
+        userAgent = userAgent.toLowerCase(Locale.ROOT);
 
         // browser engine name
         isGecko = userAgent.indexOf("gecko") != -1
diff --git a/shared/src/main/java/com/vaadin/shared/ui/PreloadMode.java b/shared/src/main/java/com/vaadin/shared/ui/PreloadMode.java
index 111278fb0c..2c6f826817 100644
--- a/shared/src/main/java/com/vaadin/shared/ui/PreloadMode.java
+++ b/shared/src/main/java/com/vaadin/shared/ui/PreloadMode.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.shared.ui;
 
+import java.util.Locale;
+
 /**
  * Enumeration that provides a hint to the browser how media should be
  * preloaded.
@@ -44,6 +46,6 @@ public enum PreloadMode {
      * @return corresponding preload attribute value string
      */
     public String getValue() {
-        return name().toLowerCase();
+        return name().toLowerCase(Locale.ROOT);
     }
 }
diff --git a/shared/src/main/java/com/vaadin/shared/ui/dnd/criteria/Payload.java b/shared/src/main/java/com/vaadin/shared/ui/dnd/criteria/Payload.java
index fc032ab76d..45be1533b9 100644
--- a/shared/src/main/java/com/vaadin/shared/ui/dnd/criteria/Payload.java
+++ b/shared/src/main/java/com/vaadin/shared/ui/dnd/criteria/Payload.java
@@ -16,6 +16,7 @@
 package com.vaadin.shared.ui.dnd.criteria;
 
 import java.io.Serializable;
+import java.util.Locale;
 
 /**
  * Stores key/value pairs and the value type. Payload is set in
@@ -53,11 +54,11 @@ public class Payload implements Serializable {
      * Creates a payload object.
      *
      * @param key
-     *         key of the payload
+     *            key of the payload
      * @param value
-     *         value of the payload
+     *            value of the payload
      * @param valueType
-     *         type of the payload value
+     *            type of the payload value
      */
     public Payload(String key, String value, ValueType valueType) {
         this.key = key;
@@ -99,8 +100,8 @@ public class Payload implements Serializable {
      * @return the string representation of this payload
      */
     public String getPayloadString() {
-        return ITEM_PREFIX + ":" + valueType.name().toLowerCase() + ":" + key
-                + ":" + value;
+        return ITEM_PREFIX + ":" + valueType.name().toLowerCase(Locale.ROOT)
+                + ":" + key + ":" + value;
     }
 
     /**
@@ -108,7 +109,7 @@ public class Payload implements Serializable {
      * string.
      *
      * @param payloadString
-     *         string that represents a payload object
+     *            string that represents a payload object
      * @return a payload object represented by the given string
      */
     public static Payload parse(String payloadString) {
@@ -122,6 +123,6 @@ public class Payload implements Serializable {
         // Create payload object of the given parts. Value type is converted to
         // upper case to match the enum's case.
         return new Payload(parts[2], parts[3],
-                ValueType.valueOf(parts[1].toUpperCase()));
+                ValueType.valueOf(parts[1].toUpperCase(Locale.ROOT)));
     }
 }
diff --git a/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java b/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
index 9a837c1e75..988ff86f14 100644
--- a/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
+++ b/shared/src/main/java/com/vaadin/shared/util/SharedUtil.java
@@ -143,7 +143,7 @@ public class SharedUtil implements Serializable {
         String[] parts = upperCaseUnderscoreString.replaceFirst("^_*", "")
                 .split("_");
         for (int i = 0; i < parts.length; i++) {
-            parts[i] = capitalize(parts[i].toLowerCase(Locale.ENGLISH));
+            parts[i] = capitalize(parts[i].toLowerCase(Locale.ROOT));
         }
         return join(parts, " ");
     }
@@ -186,10 +186,10 @@ public class SharedUtil implements Serializable {
         }
 
         if (string.length() <= 1) {
-            return string.toUpperCase(Locale.ENGLISH);
+            return string.toUpperCase(Locale.ROOT);
         }
 
-        return string.substring(0, 1).toUpperCase(Locale.ENGLISH)
+        return string.substring(0, 1).toUpperCase(Locale.ROOT)
                 + string.substring(1);
     }
 
diff --git a/test/dependency-rewrite-addon/src/main/java/com/vaadin/test/dependencyrewriteaddon/RewriteJQueryFilter.java b/test/dependency-rewrite-addon/src/main/java/com/vaadin/test/dependencyrewriteaddon/RewriteJQueryFilter.java
index 3a317da46c..633a3ae8c9 100644
--- a/test/dependency-rewrite-addon/src/main/java/com/vaadin/test/dependencyrewriteaddon/RewriteJQueryFilter.java
+++ b/test/dependency-rewrite-addon/src/main/java/com/vaadin/test/dependencyrewriteaddon/RewriteJQueryFilter.java
@@ -19,7 +19,7 @@ public class RewriteJQueryFilter
         List<Dependency> filtered = new ArrayList<>();
         for (Dependency dependency : dependencies) {
             if (dependency.getType() == Type.JAVASCRIPT && dependency.getUrl()
-                    .toLowerCase(Locale.ENGLISH).contains("jquery")) {
+                    .toLowerCase(Locale.ROOT).contains("jquery")) {
                 filtered.add(
                         new Dependency(Type.JAVASCRIPT, "vaadin://jquery.js"));
             } else {
diff --git a/test/servlet-containers/generic-tests/src/main/java/com/vaadin/tests/integration/AbstractIntegrationTest.java b/test/servlet-containers/generic-tests/src/main/java/com/vaadin/tests/integration/AbstractIntegrationTest.java
index c05cb6fdc6..68a030ec85 100644
--- a/test/servlet-containers/generic-tests/src/main/java/com/vaadin/tests/integration/AbstractIntegrationTest.java
+++ b/test/servlet-containers/generic-tests/src/main/java/com/vaadin/tests/integration/AbstractIntegrationTest.java
@@ -3,6 +3,7 @@ package com.vaadin.tests.integration;
 import java.awt.image.BufferedImage;
 import java.io.File;
 import java.io.IOException;
+import java.util.Locale;
 import java.util.logging.Logger;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -81,10 +82,10 @@ public abstract class AbstractIntegrationTest extends ParallelTest {
 
     protected void compareScreen(String identifier) throws IOException {
         String refFileName = identifier + "-"
-                + getDesiredCapabilities().getBrowserName().toLowerCase()
+                + getDesiredCapabilities().getBrowserName().toLowerCase(Locale.ROOT)
                 + ".png";
         String errorFileName = identifier + "-"
-                + getDesiredCapabilities().getBrowserName().toLowerCase() + "-"
+                + getDesiredCapabilities().getBrowserName().toLowerCase(Locale.ROOT) + "-"
                 + System.getProperty("server-name") + "["
                 + getClass().getSimpleName() + "].png";
         File referenceFile = ImageFileUtil
diff --git a/testbench-api/src/main/java/com/vaadin/testbench/elements/AbstractComponentElement.java b/testbench-api/src/main/java/com/vaadin/testbench/elements/AbstractComponentElement.java
index a95cc58106..b91f3994d1 100644
--- a/testbench-api/src/main/java/com/vaadin/testbench/elements/AbstractComponentElement.java
+++ b/testbench-api/src/main/java/com/vaadin/testbench/elements/AbstractComponentElement.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.testbench.elements;
 
+import java.util.Locale;
+
 import org.openqa.selenium.WebElement;
 
 import com.vaadin.testbench.By;
@@ -69,7 +71,7 @@ public class AbstractComponentElement extends AbstractElement {
         String[] styles = style.split(";");
         for (String stylePart : styles) {
             // IE8 has uppercased styles
-            String lowercasePart = stylePart.toLowerCase();
+            String lowercasePart = stylePart.toLowerCase(Locale.ROOT);
             if (lowercasePart.startsWith(styleName + ":")) {
                 return lowercasePart.substring(styleName.length() + 1).trim();
             }
diff --git a/uitest/src/main/java/com/vaadin/launcher/util/BrowserLauncher.java b/uitest/src/main/java/com/vaadin/launcher/util/BrowserLauncher.java
index cf26d4a891..5abc77e3ff 100644
--- a/uitest/src/main/java/com/vaadin/launcher/util/BrowserLauncher.java
+++ b/uitest/src/main/java/com/vaadin/launcher/util/BrowserLauncher.java
@@ -21,6 +21,7 @@ import java.io.BufferedReader;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.util.Locale;
 
 /**
  * This class opens default browser for DemoLauncher class. Default browser is
@@ -40,7 +41,7 @@ public class BrowserLauncher {
         boolean started = false;
 
         final String os = System.getProperty("os.name", "windows")
-                .toLowerCase();
+                .toLowerCase(Locale.ROOT);
 
         // Linux
         if (os.indexOf("linux") >= 0) {
diff --git a/uitest/src/main/java/com/vaadin/tests/TestBench.java b/uitest/src/main/java/com/vaadin/tests/TestBench.java
index b7b8c93177..208f583dc3 100644
--- a/uitest/src/main/java/com/vaadin/tests/TestBench.java
+++ b/uitest/src/main/java/com/vaadin/tests/TestBench.java
@@ -22,6 +22,7 @@ import java.util.ArrayList;
 import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 import com.vaadin.server.ExternalResource;
@@ -180,8 +181,9 @@ public class TestBench extends com.vaadin.server.LegacyApplication
                                 if (next instanceof Class) {
                                     Class<?> c = (Class<?>) next;
                                     String string = c.getSimpleName();
-                                    if (string.toLowerCase()
-                                            .contains(fragment.toLowerCase())) {
+                                    if (string.toLowerCase(Locale.ROOT)
+                                            .contains(fragment.toLowerCase(
+                                                    Locale.ROOT))) {
                                         menu.setValue(c);
                                         mainLayout.setSplitPosition(0);
                                         return;
diff --git a/uitest/src/main/java/com/vaadin/tests/components/combobox/ComboBoxItemIcon.java b/uitest/src/main/java/com/vaadin/tests/components/combobox/ComboBoxItemIcon.java
index a479922b4d..ad27e2b6ab 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/combobox/ComboBoxItemIcon.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/combobox/ComboBoxItemIcon.java
@@ -1,5 +1,7 @@
 package com.vaadin.tests.components.combobox;
 
+import java.util.Locale;
+
 import com.vaadin.server.ThemeResource;
 import com.vaadin.tests.components.TestBase;
 import com.vaadin.ui.ComboBox;
@@ -21,8 +23,9 @@ public class ComboBoxItemIcon extends TestBase {
         {
             ComboBox<String> cb = new ComboBox<>();
             cb.setItems("FI", "SE");
-            cb.setItemIconGenerator(item -> new ThemeResource(
-                    "../tests-tickets/icons/" + item.toLowerCase() + ".gif"));
+            cb.setItemIconGenerator(
+                    item -> new ThemeResource("../tests-tickets/icons/"
+                            + item.toLowerCase(Locale.ROOT) + ".gif"));
 
             addComponent(cb);
         }
@@ -31,7 +34,8 @@ public class ComboBoxItemIcon extends TestBase {
             cb.setItems("Finland", "Australia", "Hungary");
             cb.setItemIconGenerator(
                     item -> new ThemeResource("../tests-tickets/icons/"
-                            + item.substring(0, 2).toLowerCase() + ".gif"));
+                            + item.substring(0, 2).toLowerCase(Locale.ROOT)
+                            + ".gif"));
 
             cb.setValue("Hungary");
             addComponent(cb);
diff --git a/uitest/src/main/java/com/vaadin/tests/components/datefield/DateFieldChangeResolution.java b/uitest/src/main/java/com/vaadin/tests/components/datefield/DateFieldChangeResolution.java
index 3e04594de3..f03c6cb54f 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/datefield/DateFieldChangeResolution.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/datefield/DateFieldChangeResolution.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.tests.components.datefield;
 
+import java.util.Locale;
+
 import com.vaadin.server.VaadinRequest;
 import com.vaadin.shared.ui.datefield.DateResolution;
 import com.vaadin.tests.components.AbstractReindeerTestUI;
@@ -42,13 +44,12 @@ public class DateFieldChangeResolution extends AbstractReindeerTestUI {
         HorizontalLayout hlayout = new HorizontalLayout();
         addComponent(hlayout);
         for (final DateResolution value : DateResolution.values()) {
-            String resolutionString = value.toString().toLowerCase();
+            String resolutionString = value.toString().toLowerCase(Locale.ROOT);
             Button button = new Button(resolutionString);
             button.addClickListener(event -> dateField.setResolution(value));
             button.setId(BUTTON_BASE_ID + resolutionString);
             hlayout.addComponent(button);
         }
-
     }
 
     @Override
diff --git a/uitest/src/main/java/com/vaadin/tests/components/datefield/DateTimeFieldChangeResolution.java b/uitest/src/main/java/com/vaadin/tests/components/datefield/DateTimeFieldChangeResolution.java
index 2bf161daf4..2a14e20467 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/datefield/DateTimeFieldChangeResolution.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/datefield/DateTimeFieldChangeResolution.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.tests.components.datefield;
 
+import java.util.Locale;
+
 import com.vaadin.server.VaadinRequest;
 import com.vaadin.shared.ui.datefield.DateTimeResolution;
 import com.vaadin.tests.components.AbstractReindeerTestUI;
@@ -41,13 +43,12 @@ public class DateTimeFieldChangeResolution extends AbstractReindeerTestUI {
         HorizontalLayout hlayout = new HorizontalLayout();
         addComponent(hlayout);
         for (final DateTimeResolution value : DateTimeResolution.values()) {
-            String resolutionString = value.toString().toLowerCase();
+            String resolutionString = value.toString().toLowerCase(Locale.ROOT);
             Button button = new Button(resolutionString);
             button.addClickListener(event -> dateField.setResolution(value));
             button.setId(BUTTON_BASE_ID + resolutionString);
             hlayout.addComponent(button);
         }
-
     }
 
     @Override
diff --git a/uitest/src/main/java/com/vaadin/tests/components/grid/GridComponents.java b/uitest/src/main/java/com/vaadin/tests/components/grid/GridComponents.java
index 92ba75869c..c8f7127f76 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/grid/GridComponents.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/grid/GridComponents.java
@@ -1,6 +1,7 @@
 package com.vaadin.tests.components.grid;
 
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.stream.IntStream;
 
@@ -54,7 +55,7 @@ public class GridComponents extends AbstractTestUIWithLog {
                     e -> Notification.show(
                             "Clicked button on row for: " + string,
                             Type.WARNING_MESSAGE));
-            button.setId(string.replace(' ', '_').toLowerCase());
+            button.setId(string.replace(' ', '_').toLowerCase(Locale.ROOT));
             return button;
         }, new ComponentRenderer()).setId("button").setCaption("Button");
         // make sure the buttons and focus outlines fit completely in a row
diff --git a/uitest/src/main/java/com/vaadin/tests/components/grid/GridEditorUI.java b/uitest/src/main/java/com/vaadin/tests/components/grid/GridEditorUI.java
index 400ff5266c..6da0a3757f 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/grid/GridEditorUI.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/grid/GridEditorUI.java
@@ -18,6 +18,7 @@ package com.vaadin.tests.components.grid;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Random;
 
 import com.vaadin.server.VaadinRequest;
@@ -51,8 +52,9 @@ public class GridEditorUI extends AbstractReindeerTestUIWithLog {
             person.setFirstName(TestDataGenerator.getFirstName(r));
             person.setLastName(TestDataGenerator.getLastName(r));
             person.getAddress().setCity(TestDataGenerator.getCity(r));
-            person.setEmail(person.getFirstName().toLowerCase() + "."
-                    + person.getLastName().toLowerCase() + "@vaadin.com");
+            person.setEmail(person.getFirstName().toLowerCase(Locale.ROOT) + "."
+                    + person.getLastName().toLowerCase(Locale.ROOT)
+                    + "@vaadin.com");
             person.setPhoneNumber(TestDataGenerator.getPhoneNumber(r));
 
             person.getAddress()
diff --git a/uitest/src/main/java/com/vaadin/tests/components/table/HeaderRightClickAfterDrag.java b/uitest/src/main/java/com/vaadin/tests/components/table/HeaderRightClickAfterDrag.java
index b4bc32ab7b..84c676b878 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/table/HeaderRightClickAfterDrag.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/table/HeaderRightClickAfterDrag.java
@@ -1,5 +1,7 @@
 package com.vaadin.tests.components.table;
 
+import java.util.Locale;
+
 import com.vaadin.server.VaadinRequest;
 import com.vaadin.shared.MouseEventDetails;
 import com.vaadin.shared.ui.ContentMode;
@@ -26,10 +28,11 @@ public class HeaderRightClickAfterDrag extends AbstractReindeerTestUI {
             public void headerClick(Table.HeaderClickEvent event) {
                 if (MouseEventDetails.MouseButton.RIGHT
                         .equals(event.getButton())) {
-                    Window window = new Window("Right-clicked:", new Label(
-                            "<center>" + event.getPropertyId().toString()
-                                    .toUpperCase() + "</center>",
-                            ContentMode.HTML));
+                    Window window = new Window("Right-clicked:",
+                            new Label("<center>"
+                                    + event.getPropertyId().toString()
+                                            .toUpperCase(Locale.ROOT)
+                                    + "</center>", ContentMode.HTML));
                     window.setPositionX(event.getClientX());
                     window.setPositionY(event.getClientY());
                     window.setResizable(false);
diff --git a/uitest/src/main/java/com/vaadin/tests/components/textfield/TextFieldsValueChangeMode.java b/uitest/src/main/java/com/vaadin/tests/components/textfield/TextFieldsValueChangeMode.java
index 71b0a801b6..8445d8e5c9 100644
--- a/uitest/src/main/java/com/vaadin/tests/components/textfield/TextFieldsValueChangeMode.java
+++ b/uitest/src/main/java/com/vaadin/tests/components/textfield/TextFieldsValueChangeMode.java
@@ -1,5 +1,7 @@
 package com.vaadin.tests.components.textfield;
 
+import java.util.Locale;
+
 import com.vaadin.data.HasValue.ValueChangeEvent;
 import com.vaadin.server.VaadinRequest;
 import com.vaadin.shared.ui.ValueChangeMode;
@@ -29,7 +31,7 @@ public class TextFieldsValueChangeMode extends AbstractTestUIWithLog {
 
     private Component createFields(Class<?> fieldClass) {
         VerticalLayout vl = new VerticalLayout();
-        String id = fieldClass.getSimpleName().toLowerCase();
+        String id = fieldClass.getSimpleName().toLowerCase(Locale.ROOT);
         try {
             AbstractField<String> f = (AbstractField<String>) fieldClass
                     .newInstance();
diff --git a/uitest/src/main/java/com/vaadin/tests/containers/TestItemSorter.java b/uitest/src/main/java/com/vaadin/tests/containers/TestItemSorter.java
index 4af48db20a..0c6da38a1e 100644
--- a/uitest/src/main/java/com/vaadin/tests/containers/TestItemSorter.java
+++ b/uitest/src/main/java/com/vaadin/tests/containers/TestItemSorter.java
@@ -2,6 +2,7 @@ package com.vaadin.tests.containers;
 
 import java.util.Collection;
 import java.util.Comparator;
+import java.util.Locale;
 
 import com.vaadin.tests.components.TestBase;
 import com.vaadin.ui.Button;
@@ -33,13 +34,15 @@ public class TestItemSorter extends TestBase {
                     Boolean b1 = ((CheckBox) o1).getValue();
                     return b1.compareTo(((CheckBox) o2).getValue());
                 } else if (o1 instanceof Button && o2 instanceof Button) {
-                    String caption1 = ((Button) o1).getCaption().toLowerCase();
-                    String caption2 = ((Button) o2).getCaption().toLowerCase();
+                    String caption1 = ((Button) o1).getCaption()
+                            .toLowerCase(Locale.ROOT);
+                    String caption2 = ((Button) o2).getCaption()
+                            .toLowerCase(Locale.ROOT);
                     return caption1.compareTo(caption2);
 
                 } else if (o1 instanceof String && o2 instanceof String) {
-                    return ((String) o1).toLowerCase()
-                            .compareTo(((String) o2).toLowerCase());
+                    return ((String) o1).toLowerCase(Locale.ROOT)
+                            .compareTo(((String) o2).toLowerCase(Locale.ROOT));
                 }
 
                 return 0;
@@ -54,8 +57,8 @@ public class TestItemSorter extends TestBase {
 
     private static void populateContainer(IndexedContainer container) {
         container.removeAllItems();
-        String[] strings = { "Text 1", "Text 2", "true", "false",
-                "Caption 1", "Caption 2" };
+        String[] strings = { "Text 1", "Text 2", "true", "false", "Caption 1",
+                "Caption 2" };
         for (String s : strings) {
             Object id = container.addItem();
             Item item = container.getItem(id);
diff --git a/uitest/src/main/java/com/vaadin/tests/themes/ButtonsTest.java b/uitest/src/main/java/com/vaadin/tests/themes/ButtonsTest.java
index 76bdb6cd13..5c42c445c0 100644
--- a/uitest/src/main/java/com/vaadin/tests/themes/ButtonsTest.java
+++ b/uitest/src/main/java/com/vaadin/tests/themes/ButtonsTest.java
@@ -1,5 +1,7 @@
 package com.vaadin.tests.themes;
 
+import java.util.Locale;
+
 import com.vaadin.server.ThemeResource;
 import com.vaadin.server.UserError;
 import com.vaadin.ui.Button;
@@ -125,7 +127,7 @@ public class ButtonsTest extends com.vaadin.server.LegacyApplication {
             } else {
                 b = new Button(style + " style");
             }
-            b.setStyleName(style.toLowerCase());
+            b.setStyleName(style.toLowerCase(Locale.ROOT));
             if (icon) {
                 b.setIcon(new ThemeResource("../runo/icons/"
                         + (largeIcons ? "64" : "16") + "/document.png"));
diff --git a/uitest/src/main/java/com/vaadin/tests/themes/valo/CommonParts.java b/uitest/src/main/java/com/vaadin/tests/themes/valo/CommonParts.java
index 4c83430832..b5cb23a867 100644
--- a/uitest/src/main/java/com/vaadin/tests/themes/valo/CommonParts.java
+++ b/uitest/src/main/java/com/vaadin/tests/themes/valo/CommonParts.java
@@ -15,6 +15,8 @@
  */
 package com.vaadin.tests.themes.valo;
 
+import java.util.Locale;
+
 import com.vaadin.event.ShortcutAction.KeyCode;
 import com.vaadin.icons.VaadinIcons;
 import com.vaadin.navigator.View;
@@ -185,7 +187,8 @@ public class CommonParts extends VerticalLayout implements View {
                             typeString = "";
                             notification.setStyleName(styleString.trim());
                         } else {
-                            typeString = selectedItem.getText().toLowerCase();
+                            typeString = selectedItem.getText()
+                                    .toLowerCase(Locale.ROOT);
                             notification.setStyleName(
                                     (typeString + " " + styleString.trim())
                                             .trim());
@@ -214,8 +217,8 @@ public class CommonParts extends VerticalLayout implements View {
                         styleString = "";
                         for (MenuItem item : style.getItems()) {
                             if (item.isChecked()) {
-                                styleString += " "
-                                        + item.getText().toLowerCase();
+                                styleString += " " + item.getText()
+                                        .toLowerCase(Locale.ROOT);
                             }
                         }
                         if (!styleString.trim().isEmpty()) {
@@ -603,7 +606,8 @@ public class CommonParts extends VerticalLayout implements View {
                         if (selectedItem.getText()
                                 .equals("Borderless Toolbars")) {
                             toolbarStyle = selectedItem.isChecked()
-                                    ? ValoTheme.MENUBAR_BORDERLESS : null;
+                                    ? ValoTheme.MENUBAR_BORDERLESS
+                                    : null;
                         }
 
                         win.setContent(windowContent());
@@ -638,8 +642,9 @@ public class CommonParts extends VerticalLayout implements View {
                     @Override
                     public void menuSelected(MenuItem selectedItem) {
                         if (selectedItem.getText().equals("Caption")) {
-                            win.setCaption(selectedItem.isChecked()
-                                    ? "Window Caption" : null);
+                            win.setCaption(
+                                    selectedItem.isChecked() ? "Window Caption"
+                                            : null);
                         } else if (selectedItem.getText().equals("Closable")) {
                             win.setClosable(selectedItem.isChecked());
                         } else if (selectedItem.getText().equals("Resizable")) {
diff --git a/uitest/src/main/java/com/vaadin/tests/util/PersonContainer.java b/uitest/src/main/java/com/vaadin/tests/util/PersonContainer.java
index bdb73234ba..2ac37a07f7 100644
--- a/uitest/src/main/java/com/vaadin/tests/util/PersonContainer.java
+++ b/uitest/src/main/java/com/vaadin/tests/util/PersonContainer.java
@@ -4,6 +4,7 @@ import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Random;
 
 import com.vaadin.v7.data.util.BeanItemContainer;
@@ -56,8 +57,8 @@ public class PersonContainer extends BeanItemContainer<Person>
             p.setFirstName(TestDataGenerator.getFirstName(r));
             p.setLastName(TestDataGenerator.getLastName(r));
             p.getAddress().setCity(TestDataGenerator.getCity(r));
-            p.setEmail(p.getFirstName().toLowerCase() + "."
-                    + p.getLastName().toLowerCase() + "@vaadin.com");
+            p.setEmail(p.getFirstName().toLowerCase(Locale.ROOT) + "."
+                    + p.getLastName().toLowerCase(Locale.ROOT) + "@vaadin.com");
             p.setPhoneNumber(TestDataGenerator.getPhoneNumber(r));
 
             p.getAddress().setPostalCode(TestDataGenerator.getPostalCode(r));
diff --git a/uitest/src/main/java/com/vaadin/tests/widgetset/client/SerializerTestConnector.java b/uitest/src/main/java/com/vaadin/tests/widgetset/client/SerializerTestConnector.java
index 797aed66cb..037fc049a8 100644
--- a/uitest/src/main/java/com/vaadin/tests/widgetset/client/SerializerTestConnector.java
+++ b/uitest/src/main/java/com/vaadin/tests/widgetset/client/SerializerTestConnector.java
@@ -23,6 +23,7 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -169,8 +170,8 @@ public class SerializerTestConnector extends AbstractExtensionConnector {
             public void sendChar(char value, Character boxedValue,
                     char[] array) {
                 rpc.sendChar(Character.toUpperCase(boxedValue.charValue()),
-                        Character.valueOf(value),
-                        new String(array).toLowerCase().toCharArray());
+                        Character.valueOf(value), new String(array)
+                                .toLowerCase(Locale.ROOT).toCharArray());
             }
 
             @Override
diff --git a/uitest/src/main/java/com/vaadin/v7/tests/components/textfield/TextChangeEvents2.java b/uitest/src/main/java/com/vaadin/v7/tests/components/textfield/TextChangeEvents2.java
index 4dd7dfd527..7e32692e58 100644
--- a/uitest/src/main/java/com/vaadin/v7/tests/components/textfield/TextChangeEvents2.java
+++ b/uitest/src/main/java/com/vaadin/v7/tests/components/textfield/TextChangeEvents2.java
@@ -1,5 +1,7 @@
 package com.vaadin.v7.tests.components.textfield;
 
+import java.util.Locale;
+
 import com.vaadin.event.FieldEvents.BlurEvent;
 import com.vaadin.event.FieldEvents.BlurListener;
 import com.vaadin.event.FieldEvents.FocusEvent;
@@ -108,7 +110,7 @@ public class TextChangeEvents2 extends TestBase {
 
                 @Override
                 public void textChange(TextChangeEvent event) {
-                    tf.setValue(event.getText().toUpperCase());
+                    tf.setValue(event.getText().toUpperCase(Locale.ROOT));
                 }
             });
 
@@ -122,8 +124,8 @@ public class TextChangeEvents2 extends TestBase {
         }
 
         {
-            final TextField[] tfs = { new TextField(),
-                    new TextField(), new TextField(), new TextField() };
+            final TextField[] tfs = { new TextField(), new TextField(),
+                    new TextField(), new TextField() };
             HorizontalLayout hl = new HorizontalLayout();
             hl.setCaption("Blää");
             getLayout().addComponent(hl);
diff --git a/uitest/src/test/java/com/vaadin/tests/binder/BinderValidatorErrorLevelTest.java b/uitest/src/test/java/com/vaadin/tests/binder/BinderValidatorErrorLevelTest.java
index 4be9f9a49e..20b788a125 100644
--- a/uitest/src/test/java/com/vaadin/tests/binder/BinderValidatorErrorLevelTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/binder/BinderValidatorErrorLevelTest.java
@@ -1,6 +1,7 @@
 package com.vaadin.tests.binder;
 
 import java.io.IOException;
+import java.util.Locale;
 
 import org.junit.Assert;
 import org.junit.Test;
@@ -22,20 +23,23 @@ public class BinderValidatorErrorLevelTest extends SingleBrowserTest {
 
             // Screenshot the whole slot
             compareScreen(textField.findElement(By.xpath("..")),
-                    l.name().toLowerCase());
+                    l.name().toLowerCase(Locale.ROOT));
 
             Assert.assertTrue("Error style for " + l.name() + " not present",
-                    textField.getAttribute("class").contains(
-                            "v-textfield-error-" + l.name().toLowerCase()));
+                    textField.getAttribute("class")
+                            .contains("v-textfield-error-"
+                                    + l.name().toLowerCase(Locale.ROOT)));
             textField.setValue("long enough text");
             Assert.assertFalse("Error style for " + l.name() + " still present",
-                    textField.getAttribute("class").contains(
-                            "v-textfield-error-" + l.name().toLowerCase()));
+                    textField.getAttribute("class")
+                            .contains("v-textfield-error-"
+                                    + l.name().toLowerCase(Locale.ROOT)));
             textField.setValue("foo");
             Assert.assertTrue(
                     "Error style for " + l.name() + " should be present again.",
-                    textField.getAttribute("class").contains(
-                            "v-textfield-error-" + l.name().toLowerCase()));
+                    textField.getAttribute("class")
+                            .contains("v-textfield-error-"
+                                    + l.name().toLowerCase(Locale.ROOT)));
         }
     }
 }
diff --git a/uitest/src/test/java/com/vaadin/tests/components/ErrorLevelsTest.java b/uitest/src/test/java/com/vaadin/tests/components/ErrorLevelsTest.java
index 2dc9e02914..647c9601e4 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/ErrorLevelsTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/ErrorLevelsTest.java
@@ -6,6 +6,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 
 import org.junit.Test;
 import org.openqa.selenium.Keys;
@@ -133,7 +134,7 @@ public class ErrorLevelsTest extends SingleBrowserTest {
 
     private String getErrorLevelClassName(String prefix,
             ErrorLevel errorLevel) {
-        return prefix + "-" + errorLevel.toString().toLowerCase();
+        return prefix + "-" + errorLevel.toString().toLowerCase(Locale.ROOT);
     }
 
     private List<String> getErrorLevelClassNames(String prefix,
@@ -147,7 +148,8 @@ public class ErrorLevelsTest extends SingleBrowserTest {
 
     private void selectErrorLevel(ErrorLevel errorLevel) {
         errorLevelSelector.clear();
-        errorLevelSelector.sendKeys(errorLevel.toString().toLowerCase());
+        errorLevelSelector
+                .sendKeys(errorLevel.toString().toLowerCase(Locale.ROOT));
         errorLevelSelector.sendKeys(getReturn());
     }
 
diff --git a/uitest/src/test/java/com/vaadin/tests/components/checkboxgroup/CheckBoxGroupTest.java b/uitest/src/test/java/com/vaadin/tests/components/checkboxgroup/CheckBoxGroupTest.java
index 36367e4b66..b5883d43b9 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/checkboxgroup/CheckBoxGroupTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/checkboxgroup/CheckBoxGroupTest.java
@@ -24,6 +24,7 @@ import static org.junit.Assert.assertTrue;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Collectors;
 
 import org.junit.Before;
@@ -260,11 +261,11 @@ public class CheckBoxGroupTest extends MultiBrowserTest {
         for (int i = 0; i < optionsCssClasses.size(); i++) {
             String cssClassList = optionsCssClasses.get(i);
             if (i == 10) {
-                assertTrue("10th item should be disabled",
-                        cssClassList.toLowerCase().contains("disabled"));
+                assertTrue("10th item should be disabled", cssClassList
+                        .toLowerCase(Locale.ROOT).contains("disabled"));
             } else {
-                assertFalse("Only 10th item should be disabled",
-                        cssClassList.toLowerCase().contains("disabled"));
+                assertFalse("Only 10th item should be disabled", cssClassList
+                        .toLowerCase(Locale.ROOT).contains("disabled"));
             }
         }
     }
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/GridColspansTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/GridColspansTest.java
index 27b9e805bd..306e0cbe3f 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/GridColspansTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/GridColspansTest.java
@@ -57,14 +57,14 @@ public class GridColspansTest extends MultiBrowserTest {
 
         GridElement grid = $(GridElement.class).first();
         assertEquals("Failed initial condition.", "all the stuff",
-                grid.getHeaderCell(0, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(0, 1).getText().toLowerCase(Locale.ROOT));
         assertEquals("Failed initial condition.", "first name",
-                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ROOT));
         $(ButtonElement.class).caption("Show/Hide firstName").first().click();
         assertEquals("Header text changed on column hide.", "all the stuff",
-                grid.getHeaderCell(0, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(0, 1).getText().toLowerCase(Locale.ROOT));
         assertEquals("Failed initial condition.", "last name",
-                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -74,17 +74,17 @@ public class GridColspansTest extends MultiBrowserTest {
         GridElement grid = $(GridElement.class).first();
 
         assertEquals("Failed initial condition.", "first name",
-                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ROOT));
 
         $(ButtonElement.class).caption("Show/Hide firstName").first().click();
 
         assertEquals("Failed initial condition.", "last name",
-                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ROOT));
 
         $(ButtonElement.class).caption("Show/Hide firstName").first().click();
 
         assertEquals("Failed to find first name in last column", "first name",
-                grid.getHeaderCell(2, 5).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 5).getText().toLowerCase(Locale.ROOT));
 
     }
 
@@ -95,18 +95,18 @@ public class GridColspansTest extends MultiBrowserTest {
         GridElement grid = $(GridElement.class).first();
         GridCellElement headerCell = grid.getHeaderCell(1, 1);
         assertEquals("Failed initial condition.", "full name",
-                headerCell.getText().toLowerCase(Locale.ENGLISH));
+                headerCell.getText().toLowerCase(Locale.ROOT));
         assertEquals("Failed initial condition.", "first name",
-                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ENGLISH));
+                grid.getHeaderCell(2, 1).getText().toLowerCase(Locale.ROOT));
         $(ButtonElement.class).get(1).click();
         headerCell = grid.getHeaderCell(1, 1);
         assertEquals("Joined Header text not changed on column reorder.",
-                "misc", headerCell.getText().toLowerCase(Locale.ENGLISH));
+                "misc", headerCell.getText().toLowerCase(Locale.ROOT));
         assertEquals("Unexpected colspan", "1",
                 headerCell.getAttribute("colspan"));
         headerCell = grid.getHeaderCell(1, 2);
         assertEquals("Header text not changed on column reorder", "full name",
-                headerCell.getText().toLowerCase(Locale.ENGLISH));
+                headerCell.getText().toLowerCase(Locale.ROOT));
         assertEquals("Unexpected colspan", "2",
                 headerCell.getAttribute("colspan"));
 
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/GridComponentsTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/GridComponentsTest.java
index 88b218e6bf..4a303ddfb5 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/GridComponentsTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/GridComponentsTest.java
@@ -4,6 +4,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Locale;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
@@ -142,7 +143,9 @@ public class GridComponentsTest extends MultiBrowserTest {
         GridRowElement row = $(GridElement.class).first().getRow(i);
         assertEquals("Label text did not match", string,
                 row.getCell(0).getText());
-        row.findElement(By.id(string.replace(' ', '_').toLowerCase())).click();
+        row.findElement(
+                By.id(string.replace(' ', '_').toLowerCase(Locale.ROOT)))
+                .click();
         // IE 11 is slow, need to wait for the notification.
         waitUntil(driver -> isElementPresent(NotificationElement.class), 10);
         assertTrue("Notification should contain given text",
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/GridGeneratedPropertiesTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/GridGeneratedPropertiesTest.java
index df89f217f3..c2c28c75df 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/GridGeneratedPropertiesTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/GridGeneratedPropertiesTest.java
@@ -19,6 +19,8 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Locale;
+
 import org.junit.Test;
 
 import com.vaadin.testbench.elements.GridElement;
@@ -35,7 +37,7 @@ public class GridGeneratedPropertiesTest extends MultiBrowserTest {
         openTestURL();
         GridElement grid = $(GridElement.class).first();
         assertEquals("Miles header wasn't present.", "miles",
-                grid.getHeaderCell(0, 2).getText().toLowerCase());
+                grid.getHeaderCell(0, 2).getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/GridMultiSelectionScrollBarTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/GridMultiSelectionScrollBarTest.java
index 93935f7524..4c4f4595c4 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/GridMultiSelectionScrollBarTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/GridMultiSelectionScrollBarTest.java
@@ -18,6 +18,7 @@ package com.vaadin.tests.components.grid;
 import static org.junit.Assert.assertTrue;
 
 import java.io.IOException;
+import java.util.Locale;
 
 import org.junit.Test;
 
@@ -33,7 +34,7 @@ public class GridMultiSelectionScrollBarTest extends MultiBrowserTest {
 
         assertTrue("Horizontal scrollbar should not be visible.",
                 $(GridElement.class).first().getHorizontalScroller()
-                        .getAttribute("style").toLowerCase()
+                        .getAttribute("style").toLowerCase(Locale.ROOT)
                         .contains("display: none;"));
 
         // Just to make sure nothing odd happened.
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridBasicsTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridBasicsTest.java
index caec06b3f5..67c196a4e9 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridBasicsTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridBasicsTest.java
@@ -5,6 +5,7 @@ import static org.junit.Assert.assertTrue;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Stream;
 
 import org.junit.Before;
@@ -150,8 +151,8 @@ public abstract class GridBasicsTest extends MultiBrowserTest {
 
     protected void assertColumnHeader(String expectedHeaderCaption,
             TestBenchElement testBenchElement) {
-        assertEquals(expectedHeaderCaption.toLowerCase(),
-                testBenchElement.getText().toLowerCase());
+        assertEquals(expectedHeaderCaption.toLowerCase(Locale.ROOT),
+                testBenchElement.getText().toLowerCase(Locale.ROOT));
     }
 
     protected void assertColumnIsSorted(int index) {
@@ -199,7 +200,8 @@ public abstract class GridBasicsTest extends MultiBrowserTest {
         List<WebElement> elements = sidebar
                 .findElements(By.className("column-hiding-toggle"));
         for (WebElement e : elements) {
-            if (e.getText().toLowerCase().startsWith("column " + columnIndex)) {
+            if (e.getText().toLowerCase(Locale.ROOT)
+                    .startsWith("column " + columnIndex)) {
                 return e;
             }
         }
diff --git a/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridHeaderFooterTest.java b/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridHeaderFooterTest.java
index b7ba76ea73..322524fc76 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridHeaderFooterTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/grid/basics/GridHeaderFooterTest.java
@@ -20,6 +20,7 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.IntStream;
 
 import org.junit.Test;
@@ -157,7 +158,8 @@ public class GridHeaderFooterTest extends GridBasicsTest {
                 "Text Header");
         GridCellElement textCell = getGridElement().getHeaderCell(0, 2);
 
-        assertEquals("text header", textCell.getText().toLowerCase());
+        assertEquals("text header",
+                textCell.getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -180,16 +182,16 @@ public class GridHeaderFooterTest extends GridBasicsTest {
         assertTrue("No notifications should've been shown",
                 !$(NotificationElement.class).exists());
         assertEquals("Header should've been reverted back to text header",
-                "text header",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+                "text header", getGridElement().getHeaderCell(0, 1).getText()
+                        .toLowerCase(Locale.ROOT));
     }
 
     @Test
     public void testColumnHidingToggleCaption_settingWidgetToHeader_toggleCaptionStays() {
         toggleColumnHidable(1);
         getSidebarOpenButton().click();
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 1).getText()
+                .toLowerCase(Locale.ROOT));
         assertEquals("Column 1", getColumnHidingToggle(1).getText());
 
         selectMenuPath("Component", "Columns", "Column 1", "Header Type",
@@ -218,7 +220,8 @@ public class GridHeaderFooterTest extends GridBasicsTest {
                 "Text Footer");
         GridCellElement textCell = getGridElement().getFooterCell(0, 2);
 
-        assertEquals("text footer", textCell.getText().toLowerCase());
+        assertEquals("text footer",
+                textCell.getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -241,16 +244,16 @@ public class GridHeaderFooterTest extends GridBasicsTest {
         assertTrue("No notifications should've been shown",
                 !$(NotificationElement.class).exists());
         assertEquals("Footer should've been reverted back to text footer",
-                "text footer",
-                getGridElement().getFooterCell(0, 1).getText().toLowerCase());
+                "text footer", getGridElement().getFooterCell(0, 1).getText()
+                        .toLowerCase(Locale.ROOT));
     }
 
     @Test
     public void testColumnHidingToggleCaption_settingWidgetToFooter_toggleCaptionStays() {
         toggleColumnHidable(1);
         getSidebarOpenButton().click();
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 1).getText()
+                .toLowerCase(Locale.ROOT));
         assertEquals("Column 1", getColumnHidingToggle(1).getText());
 
         selectMenuPath("Component", "Columns", "Column 1", "Footer Type",
diff --git a/uitest/src/test/java/com/vaadin/tests/components/table/ColumnReorderingWithManyColumnsTest.java b/uitest/src/test/java/com/vaadin/tests/components/table/ColumnReorderingWithManyColumnsTest.java
index 98b10b9ce0..5e5773fc3f 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/table/ColumnReorderingWithManyColumnsTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/table/ColumnReorderingWithManyColumnsTest.java
@@ -3,6 +3,7 @@ package com.vaadin.tests.components.table;
 import static org.junit.Assert.assertEquals;
 
 import java.io.IOException;
+import java.util.Locale;
 
 import org.junit.Test;
 import org.openqa.selenium.By;
@@ -25,7 +26,7 @@ public class ColumnReorderingWithManyColumnsTest extends MultiBrowserTest {
                 .findElement(By.className("v-table-focus-slot-right"));
         String markedColumnName = markedElement.findElement(By.xpath(".."))
                 .getText();
-        assertEquals("col-9", markedColumnName.toLowerCase());
+        assertEquals("col-9", markedColumnName.toLowerCase(Locale.ROOT));
     }
 
     private void drag(WebElement source, WebElement target) {
diff --git a/uitest/src/test/java/com/vaadin/tests/components/ui/UIAutoGeneratedStyleNameTest.java b/uitest/src/test/java/com/vaadin/tests/components/ui/UIAutoGeneratedStyleNameTest.java
index 73dfc8f77e..3f7ab9c098 100644
--- a/uitest/src/test/java/com/vaadin/tests/components/ui/UIAutoGeneratedStyleNameTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/components/ui/UIAutoGeneratedStyleNameTest.java
@@ -39,7 +39,7 @@ public class UIAutoGeneratedStyleNameTest extends MultiBrowserTest {
         assertTrue("UI div element doesn't contain autogenerated style name",
                 containsStyle(getDriver().findElement(By.className("v-app")),
                         UIAutoGeneratedStyleName.class.getSimpleName()
-                                .toLowerCase(Locale.ENGLISH)));
+                                .toLowerCase(Locale.ROOT)));
 
         assertTrue(
                 "Overlays div element doesn't contain autogenerated style name",
@@ -47,7 +47,7 @@ public class UIAutoGeneratedStyleNameTest extends MultiBrowserTest {
                         getDriver().findElement(
                                 By.className("v-overlay-container")),
                         UIAutoGeneratedStyleName.class.getSimpleName()
-                                .toLowerCase(Locale.ENGLISH)));
+                                .toLowerCase(Locale.ROOT)));
     }
 
     private boolean containsStyle(WebElement element, String style) {
diff --git a/uitest/src/test/java/com/vaadin/tests/fieldgroup/BasicCrudGridEditorRowTest.java b/uitest/src/test/java/com/vaadin/tests/fieldgroup/BasicCrudGridEditorRowTest.java
index f23f087b40..655d046166 100644
--- a/uitest/src/test/java/com/vaadin/tests/fieldgroup/BasicCrudGridEditorRowTest.java
+++ b/uitest/src/test/java/com/vaadin/tests/fieldgroup/BasicCrudGridEditorRowTest.java
@@ -19,6 +19,8 @@ import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Locale;
+
 import org.junit.Before;
 import org.junit.Test;
 import org.openqa.selenium.By;
@@ -105,7 +107,8 @@ public class BasicCrudGridEditorRowTest extends MultiBrowserTest {
         // Open editor row
         new Actions(getDriver()).doubleClick(cell).perform();
 
-        String attribute = grid.getEditor().getAttribute("style").toLowerCase();
+        String attribute = grid.getEditor().getAttribute("style")
+                .toLowerCase(Locale.ROOT);
         assertFalse("Style should not contain top.",
                 attribute.contains("top:"));
     }
diff --git a/uitest/src/test/java/com/vaadin/tests/tb3/AffectedTB3TestLocator.java b/uitest/src/test/java/com/vaadin/tests/tb3/AffectedTB3TestLocator.java
index 9f8a79859d..016a246d40 100644
--- a/uitest/src/test/java/com/vaadin/tests/tb3/AffectedTB3TestLocator.java
+++ b/uitest/src/test/java/com/vaadin/tests/tb3/AffectedTB3TestLocator.java
@@ -19,6 +19,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 public class AffectedTB3TestLocator extends TB3TestLocator {
@@ -65,7 +66,8 @@ public class AffectedTB3TestLocator extends TB3TestLocator {
             String lastPart = packageParts[packageParts.length - 2];
 
             for (String f : affectedFiles) {
-                if (f.toLowerCase().contains(lastPart.toLowerCase())) {
+                if (f.toLowerCase(Locale.ROOT)
+                        .contains(lastPart.toLowerCase(Locale.ROOT))) {
                     affectedTestClasses.add(c);
 
                     // Break here not to accidentally add the same test class
@@ -82,7 +84,7 @@ public class AffectedTB3TestLocator extends TB3TestLocator {
         List<String> affectedFilePaths = new ArrayList<>();
 
         for (String path : changedTB3TestLocator.getChangedFilePaths()) {
-            if (!path.toLowerCase().contains("test")) {
+            if (!path.toLowerCase(Locale.ROOT).contains("test")) {
                 affectedFilePaths.add(path);
             }
         }
diff --git a/uitest/src/test/java/com/vaadin/tests/tb3/ChangedTB3TestLocator.java b/uitest/src/test/java/com/vaadin/tests/tb3/ChangedTB3TestLocator.java
index 98a98ffae0..8b3967f087 100644
--- a/uitest/src/test/java/com/vaadin/tests/tb3/ChangedTB3TestLocator.java
+++ b/uitest/src/test/java/com/vaadin/tests/tb3/ChangedTB3TestLocator.java
@@ -19,6 +19,7 @@ import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 
 import org.eclipse.jgit.api.DiffCommand;
 import org.eclipse.jgit.api.Git;
@@ -153,8 +154,8 @@ public class ChangedTB3TestLocator extends TB3TestLocator {
         List<String> changedTestFilePaths = new ArrayList<>();
 
         for (String filePath : getChangedFilePaths()) {
-            if (filePath.toLowerCase().startsWith("uitest")
-                    && filePath.toLowerCase().endsWith(".java")) {
+            if (filePath.toLowerCase(Locale.ROOT).startsWith("uitest")
+                    && filePath.toLowerCase(Locale.ROOT).endsWith(".java")) {
                 changedTestFilePaths.add(filePath);
             }
         }
diff --git a/uitest/src/test/java/com/vaadin/tests/tb3/ParameterizedTB3Runner.java b/uitest/src/test/java/com/vaadin/tests/tb3/ParameterizedTB3Runner.java
index 20107f8058..9cadcece10 100644
--- a/uitest/src/test/java/com/vaadin/tests/tb3/ParameterizedTB3Runner.java
+++ b/uitest/src/test/java/com/vaadin/tests/tb3/ParameterizedTB3Runner.java
@@ -77,7 +77,7 @@ public class ParameterizedTB3Runner extends TB3Runner {
             // getThemes -> setTheme
             String setter = "set" + m.getName().substring("get".length());
             setter = setter.substring(0, setter.length() - 1);
-            // property = property.substring(0, 1).toLowerCase()
+            // property = property.substring(0, 1).toLowerCase(Locale.ROOT)
             // + property.substring(1);
 
             Method setterMethod;
diff --git a/uitest/src/test/java/com/vaadin/tests/tb3/PrivateTB3Configuration.java b/uitest/src/test/java/com/vaadin/tests/tb3/PrivateTB3Configuration.java
index 4a34c355ad..8e55e9140a 100644
--- a/uitest/src/test/java/com/vaadin/tests/tb3/PrivateTB3Configuration.java
+++ b/uitest/src/test/java/com/vaadin/tests/tb3/PrivateTB3Configuration.java
@@ -26,6 +26,7 @@ import java.net.NetworkInterface;
 import java.net.SocketException;
 import java.util.Calendar;
 import java.util.Enumeration;
+import java.util.Locale;
 import java.util.Properties;
 
 import org.openqa.selenium.ie.InternetExplorerDriver;
@@ -131,8 +132,9 @@ public abstract class PrivateTB3Configuration extends ScreenshotTB3Test {
     protected static DesiredCapabilities getRunLocallyCapabilities() {
         VaadinBrowserFactory factory = new VaadinBrowserFactory();
         try {
-            return factory.create(Browser.valueOf(properties
-                    .getProperty(RUN_LOCALLY_PROPERTY).toUpperCase()));
+            return factory.create(
+                    Browser.valueOf(properties.getProperty(RUN_LOCALLY_PROPERTY)
+                            .toUpperCase(Locale.ROOT)));
         } catch (Exception e) {
             System.err.println(e.getMessage());
             System.err.println("Falling back to FireFox");
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridBasicFeaturesTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridBasicFeaturesTest.java
index 7c4a5962f2..073670f75b 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridBasicFeaturesTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridBasicFeaturesTest.java
@@ -20,6 +20,7 @@ import static org.junit.Assert.assertTrue;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 
 import org.openqa.selenium.By;
 import org.openqa.selenium.JavascriptExecutor;
@@ -146,8 +147,8 @@ public abstract class GridBasicFeaturesTest extends MultiBrowserTest {
 
     protected void assertColumnHeader(String expectedHeaderCaption,
             TestBenchElement testBenchElement) {
-        assertEquals(expectedHeaderCaption.toLowerCase(),
-                testBenchElement.getText().toLowerCase());
+        assertEquals(expectedHeaderCaption.toLowerCase(Locale.ROOT),
+                testBenchElement.getText().toLowerCase(Locale.ROOT));
     }
 
     protected GridCellElement getDefaultColumnHeader(int index) {
@@ -244,7 +245,7 @@ public abstract class GridBasicFeaturesTest extends MultiBrowserTest {
         List<WebElement> elements = sidebar
                 .findElements(By.className("column-hiding-toggle"));
         for (WebElement e : elements) {
-            if ((e.getText().toLowerCase())
+            if ((e.getText().toLowerCase(Locale.ROOT))
                     .startsWith("column " + columnIndex)) {
                 return e;
             }
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridColumnHidingTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridColumnHidingTest.java
index 6531acb993..c81c024453 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridColumnHidingTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/GridColumnHidingTest.java
@@ -22,8 +22,8 @@ import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
 import java.util.List;
+import java.util.Locale;
 
-import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -827,20 +827,17 @@ public class GridColumnHidingTest extends GridBasicClientFeaturesTest {
         selectMenuPath("Component", "Row details", "Toggle details for...",
                 "Row 1");
         assertColumnHeaderOrder(0, 1, 2, 3, 4);
-        assertNotNull("Details not found",
-                getGridElement().getDetails(1));
+        assertNotNull("Details not found", getGridElement().getDetails(1));
 
         toggleHideColumnAPI(0);
 
         assertColumnHeaderOrder(1, 2, 3, 4);
-        assertNotNull("Details not found",
-                getGridElement().getDetails(1));
+        assertNotNull("Details not found", getGridElement().getDetails(1));
 
         toggleHideColumnAPI(0);
 
         assertColumnHeaderOrder(0, 1, 2, 3, 4);
-        assertNotNull("Details not found",
-                getGridElement().getDetails(1));
+        assertNotNull("Details not found", getGridElement().getDetails(1));
     }
 
     @Test
@@ -884,17 +881,13 @@ public class GridColumnHidingTest extends GridBasicClientFeaturesTest {
         toggleHideColumnAPI(1);
 
         getGridElement().scrollToRow(500);
-        assertEquals("(500, 0)",
-                getGridElement().getCell(500, 0).getText());
-        assertEquals("(500, 2)",
-                getGridElement().getCell(500, 1).getText());
+        assertEquals("(500, 0)", getGridElement().getCell(500, 0).getText());
+        assertEquals("(500, 2)", getGridElement().getCell(500, 1).getText());
 
         toggleHideColumnAPI(1);
 
-        assertEquals("(500, 0)",
-                getGridElement().getCell(500, 0).getText());
-        assertEquals("(500, 1)",
-                getGridElement().getCell(500, 1).getText());
+        assertEquals("(500, 0)", getGridElement().getCell(500, 0).getText());
+        assertEquals("(500, 1)", getGridElement().getCell(500, 1).getText());
     }
 
     @Test
@@ -902,26 +895,20 @@ public class GridColumnHidingTest extends GridBasicClientFeaturesTest {
         toggleHidableColumnAPI(0);
         toggleHidableColumnAPI(1);
 
-        assertEquals("(500, 0)",
-                getGridElement().getCell(500, 0).getText());
-        assertEquals("(500, 1)",
-                getGridElement().getCell(500, 1).getText());
+        assertEquals("(500, 0)", getGridElement().getCell(500, 0).getText());
+        assertEquals("(500, 1)", getGridElement().getCell(500, 1).getText());
 
         toggleHideColumnAPI(0);
         toggleHideColumnAPI(1);
 
-        assertEquals("(500, 2)",
-                getGridElement().getCell(500, 0).getText());
-        assertEquals("(500, 3)",
-                getGridElement().getCell(500, 1).getText());
+        assertEquals("(500, 2)", getGridElement().getCell(500, 0).getText());
+        assertEquals("(500, 3)", getGridElement().getCell(500, 1).getText());
 
         toggleHideColumnAPI(0);
         toggleHideColumnAPI(1);
 
-        assertEquals("(500, 0)",
-                getGridElement().getCell(500, 0).getText());
-        assertEquals("(500, 1)",
-                getGridElement().getCell(500, 1).getText());
+        assertEquals("(500, 0)", getGridElement().getCell(500, 0).getText());
+        assertEquals("(500, 1)", getGridElement().getCell(500, 1).getText());
     }
 
     private void loadSpannedCellsFixture() {
@@ -987,7 +974,8 @@ public class GridColumnHidingTest extends GridBasicClientFeaturesTest {
     private void verifyHeaderCellContent(int row, int column, String content) {
         GridCellElement headerCell = getGridElement().getHeaderCell(row,
                 column);
-        assertEquals(content.toLowerCase(), headerCell.getText().toLowerCase());
+        assertEquals(content.toLowerCase(Locale.ROOT),
+                headerCell.getText().toLowerCase(Locale.ROOT));
         assertTrue(headerCell.isDisplayed());
     }
 
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridFooterTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridFooterTest.java
index 906f1fedba..cea86af619 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridFooterTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridFooterTest.java
@@ -19,6 +19,8 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Locale;
+
 import org.junit.Test;
 import org.openqa.selenium.By;
 import org.openqa.selenium.WebElement;
@@ -160,7 +162,8 @@ public class GridFooterTest extends GridStaticSectionTest {
          * Reindeer has a CSS text transformation that changes the casing so
          * that we can't rely on it being what we set
          */
-        assertEquals("footer (0,0)", textCell.getText().toLowerCase());
+        assertEquals("footer (0,0)",
+                textCell.getText().toLowerCase(Locale.ROOT));
 
         GridCellElement widgetCell = getGridElement().getFooterCell(0, 1);
         assertTrue(widgetCell.isElementPresent(By.className("gwt-HTML")));
@@ -193,7 +196,8 @@ public class GridFooterTest extends GridStaticSectionTest {
          * Reindeer has a CSS text transformation that changes the casing so
          * that we can't rely on it being what we set
          */
-        assertEquals("text footer", textCell.getText().toLowerCase());
+        assertEquals("text footer",
+                textCell.getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -207,11 +211,11 @@ public class GridFooterTest extends GridStaticSectionTest {
         GridCellElement widgetCell = getGridElement().getFooterCell(0, 0);
         WebElement button = widgetCell.findElement(By.className("gwt-Button"));
 
-        assertNotEquals("clicked", button.getText().toLowerCase());
+        assertNotEquals("clicked", button.getText().toLowerCase(Locale.ROOT));
 
         new Actions(getDriver()).moveToElement(button, 5, 5).click().perform();
 
-        assertEquals("clicked", button.getText().toLowerCase());
+        assertEquals("clicked", button.getText().toLowerCase(Locale.ROOT));
     }
 
     private void assertFooterCount(int count) {
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridHeaderTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridHeaderTest.java
index 0f4a10a1af..7ece0ed729 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridHeaderTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridHeaderTest.java
@@ -21,6 +21,7 @@ import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertTrue;
 
 import java.util.Arrays;
+import java.util.Locale;
 
 import org.junit.Test;
 import org.openqa.selenium.By;
@@ -204,7 +205,8 @@ public class GridHeaderTest extends GridStaticSectionTest {
          * Reindeer has a CSS text transformation that changes the casing so
          * that we can't rely on it being what we set
          */
-        assertEquals("header (0,0)", textCell.getText().toLowerCase());
+        assertEquals("header (0,0)",
+                textCell.getText().toLowerCase(Locale.ROOT));
 
         GridCellElement widgetCell = getGridElement().getHeaderCell(0, 1);
         assertTrue(widgetCell.isElementPresent(By.className("gwt-HTML")));
@@ -235,7 +237,8 @@ public class GridHeaderTest extends GridStaticSectionTest {
          * Reindeer has a CSS text transformation that changes the casing so
          * that we can't rely on it being what we set
          */
-        assertEquals("text header", textCell.getText().toLowerCase());
+        assertEquals("text header",
+                textCell.getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -249,7 +252,7 @@ public class GridHeaderTest extends GridStaticSectionTest {
 
         new Actions(getDriver()).moveToElement(button, 5, 5).click().perform();
 
-        assertEquals("clicked", button.getText().toLowerCase());
+        assertEquals("clicked", button.getText().toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -264,11 +267,11 @@ public class GridHeaderTest extends GridStaticSectionTest {
         GridCellElement widgetCell = getGridElement().getHeaderCell(0, 0);
         WebElement button = widgetCell.findElement(By.className("gwt-Button"));
 
-        assertNotEquals("clicked", button.getText().toLowerCase());
+        assertNotEquals("clicked", button.getText().toLowerCase(Locale.ROOT));
 
         new Actions(getDriver()).moveToElement(button, 5, 5).click().perform();
 
-        assertEquals("clicked", button.getText().toLowerCase());
+        assertEquals("clicked", button.getText().toLowerCase(Locale.ROOT));
     }
 
     private void assertHeaderCount(int count) {
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridStaticSectionTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridStaticSectionTest.java
index 835e9d576c..6b9aa813de 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridStaticSectionTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/client/GridStaticSectionTest.java
@@ -17,6 +17,8 @@ package com.vaadin.v7.tests.components.grid.basicfeatures.client;
 
 import static org.junit.Assert.assertEquals;
 
+import java.util.Locale;
+
 import org.openqa.selenium.By;
 import org.openqa.selenium.WebElement;
 
@@ -88,8 +90,8 @@ public abstract class GridStaticSectionTest
 
         // IE 8 returns tags as upper case while other browsers do not, make the
         // comparison non-casesensive
-        html = html.toLowerCase();
-        text = text.toLowerCase();
+        html = html.toLowerCase(Locale.ROOT);
+        text = text.toLowerCase(Locale.ROOT);
 
         // IE 8 returns attributes without quotes, make the comparison without
         // quotes
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridColumnVisibilityTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridColumnVisibilityTest.java
index c27afc4fd0..d3f3f74f38 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridColumnVisibilityTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridColumnVisibilityTest.java
@@ -21,7 +21,8 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
-import org.junit.Assert;
+import java.util.Locale;
+
 import org.junit.Before;
 import org.junit.Test;
 
@@ -32,10 +33,10 @@ import com.vaadin.v7.tests.components.grid.basicfeatures.GridBasicFeaturesTest;
 @TestCategory("grid")
 public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
 
-    private static final String[] TOGGLE_LISTENER = { "Component",
-            "State", "ColumnVisibilityChangeListener" };
-    private static final String[] TOGGLE_HIDE_COLUMN_0 = {
-            "Component", "Columns", "Column 0", "Hidden" };
+    private static final String[] TOGGLE_LISTENER = { "Component", "State",
+            "ColumnVisibilityChangeListener" };
+    private static final String[] TOGGLE_HIDE_COLUMN_0 = { "Component",
+            "Columns", "Column 0", "Hidden" };
 
     private static final String COLUMN_0_BECAME_HIDDEN_MSG = "Visibility "
             + "changed: propertyId: Column 0, isHidden: true";
@@ -51,20 +52,20 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
 
     @Test
     public void columnIsNotShownWhenHidden() {
-        assertEquals("column 0",
-                getGridElement().getHeaderCell(0, 0).getText().toLowerCase());
+        assertEquals("column 0", getGridElement().getHeaderCell(0, 0).getText()
+                .toLowerCase(Locale.ROOT));
 
         selectMenuPath(TOGGLE_HIDE_COLUMN_0);
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 0).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 0).getText()
+                .toLowerCase(Locale.ROOT));
     }
 
     @Test
     public void columnIsShownWhenUnhidden() {
         selectMenuPath(TOGGLE_HIDE_COLUMN_0);
         selectMenuPath(TOGGLE_HIDE_COLUMN_0);
-        assertEquals("column 0",
-                getGridElement().getHeaderCell(0, 0).getText().toLowerCase());
+        assertEquals("column 0", getGridElement().getHeaderCell(0, 0).getText()
+                .toLowerCase(Locale.ROOT));
     }
 
     @Test
@@ -170,15 +171,15 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
     public void testColumnHidingToggleCaption_settingToggleCaption_updatesToggle() {
         toggleColumnHidable(1);
         getSidebarOpenButton().click();
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 1).getText()
+                .toLowerCase(Locale.ROOT));
         assertEquals("Column 1", getColumnHidingToggle(1).getText());
 
         toggleColumnHidingToggleCaptionChange(1);
 
         getSidebarOpenButton().click();
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 1).getText()
+                .toLowerCase(Locale.ROOT));
         assertEquals("Column 1 caption 0", getColumnHidingToggle(1).getText());
 
         toggleColumnHidingToggleCaptionChange(1);
@@ -190,8 +191,8 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
     public void testColumnHidingToggleCaption_settingWidgetToHeader_toggleCaptionStays() {
         toggleColumnHidable(1);
         getSidebarOpenButton().click();
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 1).getText()
+                .toLowerCase(Locale.ROOT));
         assertEquals("Column 1", getColumnHidingToggle(1).getText());
 
         selectMenuPath("Component", "Columns", "Column 1", "Header Type",
@@ -209,8 +210,8 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
                 "Change header caption");
 
         getSidebarOpenButton().click();
-        assertEquals("column 1 header 0",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1 header 0", getGridElement().getHeaderCell(0, 1)
+                .getText().toLowerCase(Locale.ROOT));
         assertEquals("Column 1 header 0", getColumnHidingToggle(1).getText());
     }
 
@@ -224,8 +225,8 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
                 "Change header caption");
 
         getSidebarOpenButton().click();
-        assertEquals("column 1 header 0",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+        assertEquals("column 1 header 0", getGridElement().getHeaderCell(0, 1)
+                .getText().toLowerCase(Locale.ROOT));
         assertEquals("Column 1 caption 0", getColumnHidingToggle(1).getText());
     }
 
@@ -322,8 +323,7 @@ public class GridColumnVisibilityTest extends GridBasicFeaturesTest {
         getColumnHidingToggle(3).click();
 
         // Make sure that the new column contains the data it should
-        assertEquals("(999, 3)",
-                getGridElement().getCell(999, 3).getText());
+        assertEquals("(999, 3)", getGridElement().getCell(999, 3).getText());
     }
 
     private void verifyColumnFrozen(int index) {
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStaticSectionComponentTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStaticSectionComponentTest.java
index ed0b4a7186..10f9173300 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStaticSectionComponentTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStaticSectionComponentTest.java
@@ -18,6 +18,8 @@ package com.vaadin.v7.tests.components.grid.basicfeatures.server;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Locale;
+
 import org.junit.Test;
 
 import com.vaadin.testbench.elements.ButtonElement;
@@ -64,8 +66,8 @@ public class GridStaticSectionComponentTest extends GridBasicFeaturesTest {
         assertTrue("No notifications should've been shown",
                 !$(NotificationElement.class).exists());
         assertEquals("Header should've been reverted back to text header",
-                "text header",
-                getGridElement().getHeaderCell(0, 1).getText().toLowerCase());
+                "text header", getGridElement().getHeaderCell(0, 1).getText()
+                        .toLowerCase(Locale.ROOT));
     }
 
 }
diff --git a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStructureTest.java b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStructureTest.java
index 53a229a4c0..1d139b67a9 100644
--- a/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStructureTest.java
+++ b/uitest/src/test/java/com/vaadin/v7/tests/components/grid/basicfeatures/server/GridStructureTest.java
@@ -24,6 +24,7 @@ import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
 import java.util.List;
+import java.util.Locale;
 
 import org.junit.Test;
 import org.openqa.selenium.NoSuchElementException;
@@ -58,11 +59,11 @@ public class GridStructureTest extends GridBasicFeaturesTest {
         setDebug(true);
         openTestURL();
 
-        assertEquals("column 0",
-                getGridElement().getHeaderCell(0, 0).getText().toLowerCase());
+        assertEquals("column 0", getGridElement().getHeaderCell(0, 0).getText()
+                .toLowerCase(Locale.ROOT));
         selectMenuPath("Component", "Columns", "Column 0", "Add / Remove");
-        assertEquals("column 1",
-                getGridElement().getHeaderCell(0, 0).getText().toLowerCase());
+        assertEquals("column 1", getGridElement().getHeaderCell(0, 0).getText()
+                .toLowerCase(Locale.ROOT));
         selectMenuPath("Component", "Columns", "Column 0", "Add / Remove");
 
         // Column 0 is now the last column in Grid.
@@ -76,14 +77,16 @@ public class GridStructureTest extends GridBasicFeaturesTest {
 
         // Column 0 should be visible
         List<TestBenchElement> cells = getGridHeaderRowCells();
-        assertEquals("column 0", cells.get(0).getText().toLowerCase());
+        assertEquals("column 0",
+                cells.get(0).getText().toLowerCase(Locale.ROOT));
 
         // Hide column 0
         selectMenuPath("Component", "Columns", "Column 0", "Add / Remove");
 
         // Column 1 should now be the first cell
         cells = getGridHeaderRowCells();
-        assertEquals("column 1", cells.get(0).getText().toLowerCase());
+        assertEquals("column 1",
+                cells.get(0).getText().toLowerCase(Locale.ROOT));
     }
 
     @Test