Refactor i18n to locale (#20153)

* Refactor `i18n` to `locale`

- Currently we're using the `i18n` variable naming for the `locale`
struct. This contains locale's specific information and cannot be used
for general i18n purpose, therefore refactoring it to `locale` makes
more sense.
- Ref: https://github.com/go-gitea/gitea/pull/20096#discussion_r906699200

* Update routers/install/install.go

templates/repo/wiki/pages.tmpl

@@ -4,11 +4,11 @@
 	<div class="ui container">
 		<h2 class="ui header df ac sb">
 			<div>
-				{{.i18n.Tr "repo.wiki.pages"}}
+				{{.locale.Tr "repo.wiki.pages"}}
 			</div>
 			<div>
 				{{if and .CanWriteWiki (not .IsRepositoryMirror)}}
-					<a class="ui green small button" href="{{.RepoLink}}/wiki?action=_new">{{.i18n.Tr "repo.wiki.new_page_button"}}</a>
+					<a class="ui green small button" href="{{.RepoLink}}/wiki?action=_new">{{.locale.Tr "repo.wiki.new_page_button"}}</a>
 				{{end}}
 			</div>
 		</h2>
@@ -20,8 +20,8 @@
 							{{svg "octicon-file"}}
 							<a href="{{$.RepoLink}}/wiki/{{.SubURL}}">{{.Name}}</a>
 						</td>
-						{{$timeSince := TimeSinceUnix .UpdatedUnix $.i18n}}
-						<td class="text right grey">{{$.i18n.Tr "repo.wiki.last_updated" $timeSince | Safe}}</td>
+						{{$timeSince := TimeSinceUnix .UpdatedUnix $.locale}}
+						<td class="text right grey">{{$.locale.Tr "repo.wiki.last_updated" $timeSince | Safe}}</td>
 					</tr>
 				{{end}}
 			</tbody>