Refactor i18n, use Locale to provide i18n/translation related functions (#18648)

* remove unnecessary web context data fields, and unify the i18n/translation related functions to `Locale`
* in development, show an error if a translation key is missing
* remove the unnecessary loops `for _, lang := range translation.AllLangs()` for every request, which improves the performance slightly
* use `ctx.Locale.Language()` instead of `ctx.Data["Lang"].(string)`
* add more comments about how the Locale/LangType fields are used

3 files changed, 7 insertions, 16 deletions

diff --git a/routers/install/install.go b/routers/install/install.go
index eb2cd23463..98eeb5f8a0 100644
--- a/routers/install/install.go
+++ b/routers/install/install.go
@@ -71,25 +71,16 @@ func Init(next http.Handler) http.Handler {
 			Render:  rnd,
 			Session: session.GetSession(req),
 			Data: map[string]interface{}{
+				"i18n":          locale,
 				"Title":         locale.Tr("install.install"),
 				"PageIsInstall": true,
 				"DbTypeNames":   getDbTypeNames(),
-				"i18n":          locale,
-				"Language":      locale.Language(),
-				"Lang":          locale.Language(),
 				"AllLangs":      translation.AllLangs(),
-				"CurrentURL":    setting.AppSubURL + req.URL.RequestURI(),
 				"PageStartTime": startTime,
 
 				"PasswordHashAlgorithms": user_model.AvailableHashAlgorithms,
 			},
 		}
-		for _, lang := range translation.AllLangs() {
-			if lang.Lang == locale.Language() {
-				ctx.Data["LangName"] = lang.Name
-				break
-			}
-		}
 		ctx.Req = context.WithContext(req, &ctx)
 		next.ServeHTTP(resp, ctx.Req)
 	})
diff --git a/routers/web/repo/blame.go b/routers/web/repo/blame.go
index 588e432e3a..e96e2142d2 100644
--- a/routers/web/repo/blame.go
+++ b/routers/web/repo/blame.go
@@ -255,7 +255,7 @@ func renderBlame(ctx *context.Context, blameParts []git.BlamePart, commitNames m
 				commitCnt++
 
 				// User avatar image
-				commitSince := timeutil.TimeSinceUnix(timeutil.TimeStamp(commit.Author.When.Unix()), ctx.Data["Lang"].(string))
+				commitSince := timeutil.TimeSinceUnix(timeutil.TimeStamp(commit.Author.When.Unix()), ctx.Locale.Language())
 
 				var avatar string
 				if commit.User != nil {
diff --git a/routers/web/repo/issue_content_history.go b/routers/web/repo/issue_content_history.go
index 75951ca25b..5b5aced6ec 100644
--- a/routers/web/repo/issue_content_history.go
+++ b/routers/web/repo/issue_content_history.go
@@ -29,7 +29,7 @@ func GetContentHistoryOverview(ctx *context.Context) {
 		return
 	}
 
-	lang := ctx.Data["Lang"].(string)
+	lang := ctx.Locale.Language()
 	editedHistoryCountMap, _ := issuesModel.QueryIssueContentHistoryEditedCountMap(db.DefaultContext, issue.ID)
 	ctx.JSON(http.StatusOK, map[string]interface{}{
 		"i18n": map[string]interface{}{
@@ -55,17 +55,17 @@ func GetContentHistoryList(ctx *context.Context) {
 	// render history list to HTML for frontend dropdown items: (name, value)
 	// name is HTML of "avatar + userName + userAction + timeSince"
 	// value is historyId
-	lang := ctx.Data["Lang"].(string)
+	lang := ctx.Locale.Language()
 	var results []map[string]interface{}
 	for _, item := range items {
 		var actionText string
 		if item.IsDeleted {
-			actionTextDeleted := i18n.Tr(lang, "repo.issues.content_history.deleted")
+			actionTextDeleted := ctx.Locale.Tr("repo.issues.content_history.deleted")
 			actionText = "<i data-history-is-deleted='1'>" + actionTextDeleted + "</i>"
 		} else if item.IsFirstCreated {
-			actionText = i18n.Tr(lang, "repo.issues.content_history.created")
+			actionText = ctx.Locale.Tr("repo.issues.content_history.created")
 		} else {
-			actionText = i18n.Tr(lang, "repo.issues.content_history.edited")
+			actionText = ctx.Locale.Tr("repo.issues.content_history.edited")
 		}
 		timeSinceText := timeutil.TimeSinceUnix(item.EditedUnix, lang)
 		results = append(results, map[string]interface{}{