Make better use of i18n (#20096)

* Prototyping

* Start work on creating offsets

* Modify tests

* Start prototyping with actual MPH

* Twiddle around

* Twiddle around comments

* Convert templates

* Fix external languages

* Fix latest translation

* Fix some test

* Tidy up code

* Use simple map

* go mod tidy

* Move back to data structure

- Uses less memory by creating for each language a map.

* Apply suggestions from code review

Co-authored-by: delvh <dev.lh@web.de>

* Add some comments

* Fix tests

* Try to fix tests

* Use en-US as defacto fallback

* Use correct slices

* refactor (#4)

* Remove TryTr, add log for missing translation key

* Refactor i18n

- Separate dev and production locale stores.
- Allow for live-reloading in dev mode.

Co-authored-by: zeripath <art27@cantab.net>

* Fix live-reloading & check for errors

* Make linter happy

* live-reload with periodic check (#5)

* Fix tests

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

templates/repo/diff/comments.tmpl

@@ -1,6 +1,6 @@
 {{range .comments}}
 
-{{ $createdStr:= TimeSinceUnix .CreatedUnix $.root.i18n.Lang }}
+{{ $createdStr:= TimeSinceUnix .CreatedUnix $.root.i18n }}
 <div class="comment" id="{{.HashTag}}">
 	{{if .OriginalAuthor }}
 		<span class="avatar"><img src="{{AppSubUrl}}/assets/img/avatar_default.png"></span>