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/projects/list.tmpl

@@ -42,7 +42,7 @@
 				<li class="item">
 					{{svg "octicon-project"}} <a href="{{$.RepoLink}}/projects/{{.ID}}">{{.Title}}</a>
 					<div class="meta">
-						{{ $closedDate:= TimeSinceUnix .ClosedDateUnix $.i18n.Lang }}
+						{{ $closedDate:= TimeSinceUnix .ClosedDateUnix $.i18n }}
 						{{if .IsClosed }}
 							{{svg "octicon-clock"}} {{$.i18n.Tr "repo.milestones.closed" $closedDate|Str2html}}
 						{{end}}

templates/repo/projects/view.tmpl

@@ -207,7 +207,7 @@
 							<div class="meta my-2">
 								<span class="text light grey">
 									#{{.Index}}
-									{{ $timeStr := TimeSinceUnix .GetLastEventTimestamp $.i18n.Lang }}
+									{{ $timeStr := TimeSinceUnix .GetLastEventTimestamp $.i18n }}
 									{{if .OriginalAuthor }}
 										{{$.i18n.Tr .GetLastEventLabelFake $timeStr (.OriginalAuthor|Escape) | Safe}}
 									{{else if gt .Poster.ID 0}}