Remove legacy unmaintained packages, refactor to support change default locale (#19308)

Remove two unmaintained vendor packages `i18n` and `paginater`. Changes:
* Rewrite `i18n` package with a more clear fallback mechanism. Fix an unstable `Tr` behavior, add more tests.
* Refactor the legacy `Paginater` to `Paginator`, test cases are kept unchanged.

Trivial enhancement (no breaking for end users):
* Use the first locale in LANGS setting option as the default, add a log to prevent from surprising users.

10 files changed, 738 insertions, 19 deletions

diff --git a/modules/context/pagination.go b/modules/context/pagination.go
index 107cbf6186..c0079c2950 100644
--- a/modules/context/pagination.go
+++ b/modules/context/pagination.go
@@ -10,19 +10,19 @@ import (
 	"net/url"
 	"strings"
 
-	"github.com/unknwon/paginater"
+	"code.gitea.io/gitea/modules/paginator"
 )
 
-// Pagination provides a pagination via Paginater and additional configurations for the link params used in rendering
+// Pagination provides a pagination via paginator.Paginator and additional configurations for the link params used in rendering
 type Pagination struct {
-	Paginater *paginater.Paginater
+	Paginater *paginator.Paginator
 	urlParams []string
 }
 
 // NewPagination creates a new instance of the Pagination struct
 func NewPagination(total, page, issueNum, numPages int) *Pagination {
 	p := &Pagination{}
-	p.Paginater = paginater.New(total, page, issueNum, numPages)
+	p.Paginater = paginator.New(total, page, issueNum, numPages)
 	return p
 }
 
@@ -53,5 +53,6 @@ func (p *Pagination) SetDefaultParams(ctx *Context) {
 	p.AddParam(ctx, "sort", "SortType")
 	p.AddParam(ctx, "q", "Keyword")
 	p.AddParam(ctx, "tab", "TabName")
+	// do not add any more uncommon params here!
 	p.AddParam(ctx, "t", "queryType")
 }
diff --git a/modules/markup/markdown/toc.go b/modules/markup/markdown/toc.go
index 189821c341..9d11b771f7 100644
--- a/modules/markup/markdown/toc.go
+++ b/modules/markup/markdown/toc.go
@@ -8,7 +8,8 @@ import (
 	"fmt"
 	"net/url"
 
-	"github.com/unknwon/i18n"
+	"code.gitea.io/gitea/modules/translation/i18n"
+
 	"github.com/yuin/goldmark/ast"
 )
 
diff --git a/modules/paginator/paginator.go b/modules/paginator/paginator.go
new file mode 100644
index 0000000000..873cfe49d4
--- /dev/null
+++ b/modules/paginator/paginator.go
@@ -0,0 +1,203 @@
+// Copyright 2022 The Gitea Authors.
+// Copyright 2015 Unknwon. Licensed under the Apache License, Version 2.0
+
+package paginator
+
+/*
+In template:
+
+```html
+{{if not .Page.IsFirst}}[First](1){{end}}
+{{if .Page.HasPrevious}}[Previous]({{.Page.Previous}}){{end}}
+
+{{range .Page.Pages}}
+	{{if eq .Num -1}}
+	...
+	{{else}}
+	{{.Num}}{{if .IsCurrent}}(current){{end}}
+	{{end}}
+{{end}}
+
+{{if .Page.HasNext}}[Next]({{.Page.Next}}){{end}}
+{{if not .Page.IsLast}}[Last]({{.Page.TotalPages}}){{end}}
+```
+
+Output:
+
+```
+[First](1) [Previous](2) ... 2 3(current) 4 ... [Next](4) [Last](5)
+```
+*/
+
+// Paginator represents a set of results of pagination calculations.
+type Paginator struct {
+	total     int // total rows count
+	pagingNum int // how many rows in one page
+	current   int // current page number
+	numPages  int // how many pages to show on the UI
+}
+
+// New initialize a new pagination calculation and returns a Paginator as result.
+func New(total, pagingNum, current, numPages int) *Paginator {
+	if pagingNum <= 0 {
+		pagingNum = 1
+	}
+	if current <= 0 {
+		current = 1
+	}
+	p := &Paginator{total, pagingNum, current, numPages}
+	if p.current > p.TotalPages() {
+		p.current = p.TotalPages()
+	}
+	return p
+}
+
+// IsFirst returns true if current page is the first page.
+func (p *Paginator) IsFirst() bool {
+	return p.current == 1
+}
+
+// HasPrevious returns true if there is a previous page relative to current page.
+func (p *Paginator) HasPrevious() bool {
+	return p.current > 1
+}
+
+func (p *Paginator) Previous() int {
+	if !p.HasPrevious() {
+		return p.current
+	}
+	return p.current - 1
+}
+
+// HasNext returns true if there is a next page relative to current page.
+func (p *Paginator) HasNext() bool {
+	return p.total > p.current*p.pagingNum
+}
+
+func (p *Paginator) Next() int {
+	if !p.HasNext() {
+		return p.current
+	}
+	return p.current + 1
+}
+
+// IsLast returns true if current page is the last page.
+func (p *Paginator) IsLast() bool {
+	if p.total == 0 {
+		return true
+	}
+	return p.total > (p.current-1)*p.pagingNum && !p.HasNext()
+}
+
+// Total returns number of total rows.
+func (p *Paginator) Total() int {
+	return p.total
+}
+
+// TotalPages returns number of total pages.
+func (p *Paginator) TotalPages() int {
+	if p.total == 0 {
+		return 1
+	}
+	return (p.total + p.pagingNum - 1) / p.pagingNum
+}
+
+// Current returns current page number.
+func (p *Paginator) Current() int {
+	return p.current
+}
+
+// PagingNum returns number of page size.
+func (p *Paginator) PagingNum() int {
+	return p.pagingNum
+}
+
+// Page presents a page in the paginator.
+type Page struct {
+	num       int
+	isCurrent bool
+}
+
+func (p *Page) Num() int {
+	return p.num
+}
+
+func (p *Page) IsCurrent() bool {
+	return p.isCurrent
+}
+
+func getMiddleIdx(numPages int) int {
+	return (numPages + 1) / 2
+}
+
+// Pages returns a list of nearby page numbers relative to current page.
+// If value is -1 means "..." that more pages are not showing.
+func (p *Paginator) Pages() []*Page {
+	if p.numPages == 0 {
+		return []*Page{}
+	} else if p.numPages == 1 && p.TotalPages() == 1 {
+		// Only show current page.
+		return []*Page{{1, true}}
+	}
+
+	// Total page number is less or equal.
+	if p.TotalPages() <= p.numPages {
+		pages := make([]*Page, p.TotalPages())
+		for i := range pages {
+			pages[i] = &Page{i + 1, i+1 == p.current}
+		}
+		return pages
+	}
+
+	numPages := p.numPages
+	offsetIdx := 0
+	hasMoreNext := false
+
+	// Check more previous and next pages.
+	previousNum := getMiddleIdx(p.numPages) - 1
+	if previousNum > p.current-1 {
+		previousNum -= previousNum - (p.current - 1)
+	}
+	nextNum := p.numPages - previousNum - 1
+	if p.current+nextNum > p.TotalPages() {
+		delta := nextNum - (p.TotalPages() - p.current)
+		nextNum -= delta
+		previousNum += delta
+	}
+
+	offsetVal := p.current - previousNum
+	if offsetVal > 1 {
+		numPages++
+		offsetIdx = 1
+	}
+
+	if p.current+nextNum < p.TotalPages() {
+		numPages++
+		hasMoreNext = true
+	}
+
+	pages := make([]*Page, numPages)
+
+	// There are more previous pages.
+	if offsetIdx == 1 {
+		pages[0] = &Page{-1, false}
+	}
+	// There are more next pages.
+	if hasMoreNext {
+		pages[len(pages)-1] = &Page{-1, false}
+	}
+
+	// Check previous pages.
+	for i := 0; i < previousNum; i++ {
+		pages[offsetIdx+i] = &Page{i + offsetVal, false}
+	}
+
+	pages[offsetIdx+previousNum] = &Page{p.current, true}
+
+	// Check next pages.
+	for i := 1; i <= nextNum; i++ {
+		pages[offsetIdx+previousNum+i] = &Page{p.current + i, false}
+	}
+
+	return pages
+}
diff --git a/modules/paginator/paginator_test.go b/modules/paginator/paginator_test.go
new file mode 100644
index 0000000000..ce7b7275e1
--- /dev/null
+++ b/modules/paginator/paginator_test.go
@@ -0,0 +1,311 @@
+// Copyright 2022 The Gitea Authors.
+// Copyright 2015 Unknwon. Licensed under the Apache License, Version 2.0
+
+package paginator
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPaginator(t *testing.T) {
+	t.Run("Basic logics", func(t *testing.T) {
+		p := New(0, -1, -1, 0)
+		assert.Equal(t, 1, p.PagingNum())
+		assert.True(t, p.IsFirst())
+		assert.False(t, p.HasPrevious())
+		assert.Equal(t, 1, p.Previous())
+		assert.False(t, p.HasNext())
+		assert.Equal(t, 1, p.Next())
+		assert.True(t, p.IsLast())
+		assert.Equal(t, 0, p.Total())
+
+		p = New(1, 10, 2, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.True(t, p.IsFirst())
+		assert.False(t, p.HasPrevious())
+		assert.False(t, p.HasNext())
+		assert.True(t, p.IsLast())
+
+		p = New(10, 10, 1, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.True(t, p.IsFirst())
+		assert.False(t, p.HasPrevious())
+		assert.False(t, p.HasNext())
+		assert.True(t, p.IsLast())
+
+		p = New(11, 10, 1, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.True(t, p.IsFirst())
+		assert.False(t, p.HasPrevious())
+		assert.True(t, p.HasNext())
+		assert.Equal(t, 2, p.Next())
+		assert.False(t, p.IsLast())
+
+		p = New(11, 10, 2, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.False(t, p.IsFirst())
+		assert.True(t, p.HasPrevious())
+		assert.Equal(t, 1, p.Previous())
+		assert.False(t, p.HasNext())
+		assert.True(t, p.IsLast())
+
+		p = New(20, 10, 2, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.False(t, p.IsFirst())
+		assert.True(t, p.HasPrevious())
+		assert.False(t, p.HasNext())
+		assert.True(t, p.IsLast())
+
+		p = New(25, 10, 2, 0)
+		assert.Equal(t, 10, p.PagingNum())
+		assert.False(t, p.IsFirst())
+		assert.True(t, p.HasPrevious())
+		assert.True(t, p.HasNext())
+		assert.False(t, p.IsLast())
+	})
+
+	t.Run("Generate pages", func(t *testing.T) {
+		p := New(0, 10, 1, 0)
+		pages := p.Pages()
+		assert.Equal(t, 0, len(pages))
+	})
+
+	t.Run("Only current page", func(t *testing.T) {
+		p := New(0, 10, 1, 1)
+		pages := p.Pages()
+		assert.Equal(t, 1, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+
+		p = New(1, 10, 1, 1)
+		pages = p.Pages()
+		assert.Equal(t, 1, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+	})
+
+	t.Run("Total page number is less or equal", func(t *testing.T) {
+		p := New(1, 10, 1, 2)
+		pages := p.Pages()
+		assert.Equal(t, 1, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+
+		p = New(11, 10, 1, 2)
+		pages = p.Pages()
+		assert.Equal(t, 2, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+
+		p = New(11, 10, 2, 2)
+		pages = p.Pages()
+		assert.Equal(t, 2, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+
+		p = New(25, 10, 2, 3)
+		pages = p.Pages()
+		assert.Equal(t, 3, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+	})
+
+	t.Run("Has more previous pages ", func(t *testing.T) {
+		// ... 2
+		p := New(11, 10, 2, 1)
+		pages := p.Pages()
+		assert.Equal(t, 2, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+
+		// ... 2 3
+		p = New(21, 10, 2, 2)
+		pages = p.Pages()
+		assert.Equal(t, 3, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+
+		// ... 2 3 4
+		p = New(31, 10, 3, 3)
+		pages = p.Pages()
+		assert.Equal(t, 4, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.True(t, pages[2].IsCurrent())
+		assert.Equal(t, 4, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+
+		// ... 3 4 5
+		p = New(41, 10, 4, 3)
+		pages = p.Pages()
+		assert.Equal(t, 4, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 3, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, 4, pages[2].Num())
+		assert.True(t, pages[2].IsCurrent())
+		assert.Equal(t, 5, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+
+		// ... 4 5 6 7 8 9 10
+		p = New(100, 10, 9, 7)
+		pages = p.Pages()
+		assert.Equal(t, 8, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 4, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, 5, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, 6, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+		assert.Equal(t, 7, pages[4].Num())
+		assert.False(t, pages[4].IsCurrent())
+		assert.Equal(t, 8, pages[5].Num())
+		assert.False(t, pages[5].IsCurrent())
+		assert.Equal(t, 9, pages[6].Num())
+		assert.True(t, pages[6].IsCurrent())
+		assert.Equal(t, 10, pages[7].Num())
+		assert.False(t, pages[7].IsCurrent())
+	})
+
+	t.Run("Has more next pages", func(t *testing.T) {
+		// 1 ...
+		p := New(21, 10, 1, 1)
+		pages := p.Pages()
+		assert.Equal(t, 2, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+		assert.Equal(t, -1, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+
+		// 1 2 ...
+		p = New(21, 10, 1, 2)
+		pages = p.Pages()
+		assert.Equal(t, 3, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, -1, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+
+		// 1 2 3 ...
+		p = New(31, 10, 2, 3)
+		pages = p.Pages()
+		assert.Equal(t, 4, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, -1, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+
+		// 1 2 3 ...
+		p = New(41, 10, 2, 3)
+		pages = p.Pages()
+		assert.Equal(t, 4, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, -1, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+
+		// 1 2 3 4 5 6 7 ...
+		p = New(100, 10, 1, 7)
+		pages = p.Pages()
+		assert.Equal(t, 8, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.True(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, 4, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+		assert.Equal(t, 5, pages[4].Num())
+		assert.False(t, pages[4].IsCurrent())
+		assert.Equal(t, 6, pages[5].Num())
+		assert.False(t, pages[5].IsCurrent())
+		assert.Equal(t, 7, pages[6].Num())
+		assert.False(t, pages[6].IsCurrent())
+		assert.Equal(t, -1, pages[7].Num())
+		assert.False(t, pages[7].IsCurrent())
+
+		// 1 2 3 4 5 6 7 ...
+		p = New(100, 10, 2, 7)
+		pages = p.Pages()
+		assert.Equal(t, 8, len(pages))
+		assert.Equal(t, 1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, 4, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+		assert.Equal(t, 5, pages[4].Num())
+		assert.False(t, pages[4].IsCurrent())
+		assert.Equal(t, 6, pages[5].Num())
+		assert.False(t, pages[5].IsCurrent())
+		assert.Equal(t, 7, pages[6].Num())
+		assert.False(t, pages[6].IsCurrent())
+		assert.Equal(t, -1, pages[7].Num())
+		assert.False(t, pages[7].IsCurrent())
+	})
+
+	t.Run("Has both more previous and next pages", func(t *testing.T) {
+		// ... 2 3 ...
+		p := New(35, 10, 2, 2)
+		pages := p.Pages()
+		assert.Equal(t, 4, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.True(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.False(t, pages[2].IsCurrent())
+		assert.Equal(t, -1, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+
+		// ... 2 3 4 ...
+		p = New(49, 10, 3, 3)
+		pages = p.Pages()
+		assert.Equal(t, 5, len(pages))
+		assert.Equal(t, -1, pages[0].Num())
+		assert.False(t, pages[0].IsCurrent())
+		assert.Equal(t, 2, pages[1].Num())
+		assert.False(t, pages[1].IsCurrent())
+		assert.Equal(t, 3, pages[2].Num())
+		assert.True(t, pages[2].IsCurrent())
+		assert.Equal(t, 4, pages[3].Num())
+		assert.False(t, pages[3].IsCurrent())
+		assert.Equal(t, -1, pages[4].Num())
+		assert.False(t, pages[4].IsCurrent())
+	})
+}
diff --git a/modules/timeutil/since.go b/modules/timeutil/since.go
index c0240907ae..38b12829ad 100644
--- a/modules/timeutil/since.go
+++ b/modules/timeutil/since.go
@@ -12,8 +12,7 @@ import (
 	"time"
 
 	"code.gitea.io/gitea/modules/setting"
-
-	"github.com/unknwon/i18n"
+	"code.gitea.io/gitea/modules/translation/i18n"
 )
 
 // Seconds-based time units
diff --git a/modules/timeutil/since_test.go b/modules/timeutil/since_test.go
index 1379e71c3d..49951b6e41 100644
--- a/modules/timeutil/since_test.go
+++ b/modules/timeutil/since_test.go
@@ -12,9 +12,9 @@ import (
 
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/translation"
+	"code.gitea.io/gitea/modules/translation/i18n"
 
 	"github.com/stretchr/testify/assert"
-	"github.com/unknwon/i18n"
 )
 
 var BaseDate time.Time
diff --git a/modules/translation/i18n/i18n.go b/modules/translation/i18n/i18n.go
new file mode 100644
index 0000000000..664e457ecf
--- /dev/null
+++ b/modules/translation/i18n/i18n.go
@@ -0,0 +1,143 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package i18n
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"gopkg.in/ini.v1"
+)
+
+var (
+	ErrLocaleAlreadyExist = errors.New("lang already exists")
+
+	DefaultLocales = NewLocaleStore()
+)
+
+type locale struct {
+	store    *LocaleStore
+	langName string
+	langDesc string
+	messages *ini.File
+}
+
+type LocaleStore struct {
+	// at the moment, all these fields are readonly after initialization
+	langNames   []string
+	langDescs   []string
+	localeMap   map[string]*locale
+	defaultLang string
+}
+
+func NewLocaleStore() *LocaleStore {
+	return &LocaleStore{localeMap: make(map[string]*locale)}
+}
+
+// AddLocaleByIni adds locale by ini into the store
+func (ls *LocaleStore) AddLocaleByIni(langName, langDesc string, localeFile interface{}, otherLocaleFiles ...interface{}) error {
+	if _, ok := ls.localeMap[langName]; ok {
+		return ErrLocaleAlreadyExist
+	}
+	iniFile, err := ini.LoadSources(ini.LoadOptions{
+		IgnoreInlineComment:         true,
+		UnescapeValueCommentSymbols: true,
+	}, localeFile, otherLocaleFiles...)
+	if err == nil {
+		iniFile.BlockMode = false
+		lc := &locale{store: ls, langName: langName, langDesc: langDesc, messages: iniFile}
+		ls.langNames = append(ls.langNames, lc.langName)
+		ls.langDescs = append(ls.langDescs, lc.langDesc)
+		ls.localeMap[lc.langName] = lc
+	}
+	return err
+}
+
+func (ls *LocaleStore) HasLang(langName string) bool {
+	_, ok := ls.localeMap[langName]
+	return ok
+}
+
+func (ls *LocaleStore) ListLangNameDesc() (names, desc []string) {
+	return ls.langNames, ls.langDescs
+}
+
+// SetDefaultLang sets default language as a fallback
+func (ls *LocaleStore) SetDefaultLang(lang string) {
+	ls.defaultLang = lang
+}
+
+// Tr translates content to target language. fall back to default language.
+func (ls *LocaleStore) Tr(lang, trKey string, trArgs ...interface{}) string {
+	l, ok := ls.localeMap[lang]
+	if !ok {
+		l, ok = ls.localeMap[ls.defaultLang]
+	}
+	if ok {
+		return l.Tr(trKey, trArgs...)
+	}
+	return trKey
+}
+
+// Tr translates content to locale language. fall back to default language.
+func (l *locale) Tr(trKey string, trArgs ...interface{}) string {
+	var section string
+
+	idx := strings.IndexByte(trKey, '.')
+	if idx > 0 {
+		section = trKey[:idx]
+		trKey = trKey[idx+1:]
+	}
+
+	trMsg := trKey
+	if trIni, err := l.messages.Section(section).GetKey(trKey); err == nil {
+		trMsg = trIni.Value()
+	} else if l.store.defaultLang != "" && l.langName != l.store.defaultLang {
+		// try to fall back to default
+		if defaultLocale, ok := l.store.localeMap[l.store.defaultLang]; ok {
+			if trIni, err = defaultLocale.messages.Section(section).GetKey(trKey); err == nil {
+				trMsg = trIni.Value()
+			}
+		}
+	}
+
+	if len(trArgs) > 0 {
+		fmtArgs := make([]interface{}, 0, len(trArgs))
+		for _, arg := range trArgs {
+			val := reflect.ValueOf(arg)
+			if val.Kind() == reflect.Slice {
+				// before, it can accept Tr(lang, key, a, [b, c], d, [e, f]) as Sprintf(msg, a, b, c, d, e, f), it's an unstable behavior
+				// now, we restrict the strange behavior and only support:
+				// 1. Tr(lang, key, [slice-items]) as Sprintf(msg, items...)
+				// 2. Tr(lang, key, args...) as Sprintf(msg, args...)
+				if len(trArgs) == 1 {
+					for i := 0; i < val.Len(); i++ {
+						fmtArgs = append(fmtArgs, val.Index(i).Interface())
+					}
+				} else {
+					log.Error("the args for i18n shouldn't contain uncertain slices, key=%q, args=%v", trKey, trArgs)
+					break
+				}
+			} else {
+				fmtArgs = append(fmtArgs, arg)
+			}
+		}
+		return fmt.Sprintf(trMsg, fmtArgs...)
+	}
+	return trMsg
+}
+
+func ResetDefaultLocales() {
+	DefaultLocales = NewLocaleStore()
+}
+
+// Tr use default locales to translate content to target language.
+func Tr(lang, trKey string, trArgs ...interface{}) string {
+	return DefaultLocales.Tr(lang, trKey, trArgs...)
+}
diff --git a/modules/translation/i18n/i18n_test.go b/modules/translation/i18n/i18n_test.go
new file mode 100644
index 0000000000..70066016cf
--- /dev/null
+++ b/modules/translation/i18n/i18n_test.go
@@ -0,0 +1,56 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package i18n
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Tr(t *testing.T) {
+	testData1 := []byte(`
+.dot.name = Dot Name
+fmt = %[1]s %[2]s
+
+[section]
+sub = Sub String
+mixed = test value; <span style="color: red\; background: none;">more text</span>
+`)
+
+	testData2 := []byte(`
+fmt = %[2]s %[1]s
+
+[section]
+sub = Changed Sub String
+`)
+
+	ls := NewLocaleStore()
+	assert.NoError(t, ls.AddLocaleByIni("lang1", "Lang1", testData1))
+	assert.NoError(t, ls.AddLocaleByIni("lang2", "Lang2", testData2))
+	ls.SetDefaultLang("lang1")
+
+	result := ls.Tr("lang1", "fmt", "a", "b")
+	assert.Equal(t, "a b", result)
+
+	result = ls.Tr("lang2", "fmt", "a", "b")
+	assert.Equal(t, "b a", result)
+
+	result = ls.Tr("lang1", "section.sub")
+	assert.Equal(t, "Sub String", result)
+
+	result = ls.Tr("lang2", "section.sub")
+	assert.Equal(t, "Changed Sub String", result)
+
+	result = ls.Tr("", ".dot.name")
+	assert.Equal(t, "Dot Name", result)
+
+	result = ls.Tr("lang2", "section.mixed")
+	assert.Equal(t, `test value; <span style="color: red; background: none;">more text</span>`, result)
+
+	langs, descs := ls.ListLangNameDesc()
+	assert.Equal(t, []string{"lang1", "lang2"}, langs)
+	assert.Equal(t, []string{"Lang1", "Lang2"}, descs)
+}
diff --git a/modules/translation/translation.go b/modules/translation/translation.go
index fd38e4d510..da9d9b9b68 100644
--- a/modules/translation/translation.go
+++ b/modules/translation/translation.go
@@ -11,8 +11,8 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/options"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/translation/i18n"
 
-	"github.com/unknwon/i18n"
 	"golang.org/x/text/language"
 )
 
@@ -54,13 +54,13 @@ func TryTr(lang, format string, args ...interface{}) (string, bool) {
 
 // InitLocales loads the locales
 func InitLocales() {
-	i18n.Reset()
+	i18n.ResetDefaultLocales()
 	localeNames, err := options.Dir("locale")
 	if err != nil {
 		log.Fatal("Failed to list locale files: %v", err)
 	}
 
-	localFiles := make(map[string][]byte)
+	localFiles := make(map[string][]byte, len(localeNames))
 	for _, name := range localeNames {
 		localFiles[name], err = options.Locale(name)
 		if err != nil {
@@ -76,16 +76,21 @@ func InitLocales() {
 	matcher = language.NewMatcher(supportedTags)
 	for i := range setting.Names {
 		key := "locale_" + setting.Langs[i] + ".ini"
-		if err = i18n.SetMessageWithDesc(setting.Langs[i], setting.Names[i], localFiles[key]); err != nil {
+		if err = i18n.DefaultLocales.AddLocaleByIni(setting.Langs[i], setting.Names[i], localFiles[key]); err != nil {
 			log.Error("Failed to set messages to %s: %v", setting.Langs[i], err)
 		}
 	}
-	i18n.SetDefaultLang("en-US")
+	if len(setting.Langs) != 0 {
+		defaultLangName := setting.Langs[0]
+		if defaultLangName != "en-US" {
+			log.Info("Use the first locale (%s) in LANGS setting option as default", defaultLangName)
+		}
+		i18n.DefaultLocales.SetDefaultLang(defaultLangName)
+	}
 
-	allLangs = make([]*LangType, 0, i18n.Count())
+	langs, descs := i18n.DefaultLocales.ListLangNameDesc()
+	allLangs = make([]*LangType, 0, len(langs))
 	allLangMap = map[string]*LangType{}
-	langs := i18n.ListLangs()
-	descs := i18n.ListLangDescs()
 	for i, v := range langs {
 		l := &LangType{v, descs[i]}
 		allLangs = append(allLangs, l)
diff --git a/modules/web/middleware/locale.go b/modules/web/middleware/locale.go
index 3daf5f32d4..de8e497965 100644
--- a/modules/web/middleware/locale.go
+++ b/modules/web/middleware/locale.go
@@ -9,8 +9,8 @@ import (
 
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/translation"
+	"code.gitea.io/gitea/modules/translation/i18n"
 
-	"github.com/unknwon/i18n"
 	"golang.org/x/text/language"
 )
 
@@ -28,8 +28,8 @@ func Locale(resp http.ResponseWriter, req *http.Request) translation.Locale {
 		}
 	}
 
-	// Check again in case someone modify by purpose.
-	if lang != "" && !i18n.IsExist(lang) {
+	// Check again in case someone changes the supported language list.
+	if lang != "" && !i18n.DefaultLocales.HasLang(lang) {
 		lang = ""
 		changeLang = false
 	}