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

modules/context/context.go

@@ -38,7 +38,6 @@ import (
 	"gitea.com/go-chi/session"
 	chi "github.com/go-chi/chi/v5"
 	"github.com/unknwon/com"
-	"github.com/unknwon/i18n"
 	"github.com/unrolled/render"
 	"golang.org/x/crypto/pbkdf2"
 )
@@ -738,15 +737,7 @@ func Contexter() func(next http.Handler) http.Handler {
 			ctx.Data["UnitProjectsGlobalDisabled"] = unit.TypeProjects.UnitGlobalDisabled()
 
 			ctx.Data["i18n"] = locale
-			ctx.Data["Tr"] = i18n.Tr
-			ctx.Data["Lang"] = locale.Language()
 			ctx.Data["AllLangs"] = translation.AllLangs()
-			for _, lang := range translation.AllLangs() {
-				if lang.Lang == locale.Language() {
-					ctx.Data["LangName"] = lang.Name
-					break
-				}
-			}
 
 			next.ServeHTTP(ctx.Resp, ctx.Req)