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/org/settings/navbar.tmpl

@@ -1,19 +1,19 @@
 <div class="four wide column">
 	<div class="ui fluid vertical menu">
-		<div class="header item">{{.i18n.Tr "org.settings"}}</div>
+		<div class="header item">{{.locale.Tr "org.settings"}}</div>
 		<a class="{{if .PageIsSettingsOptions}}active{{end}} item" href="{{.OrgLink}}/settings">
-			{{.i18n.Tr "org.settings.options"}}
+			{{.locale.Tr "org.settings.options"}}
 		</a>
 		{{if not DisableWebhooks}}
 		<a class="{{if .PageIsSettingsHooks}}active{{end}} item" href="{{.OrgLink}}/settings/hooks">
-			{{.i18n.Tr "repo.settings.hooks"}}
+			{{.locale.Tr "repo.settings.hooks"}}
 		</a>
 		{{end}}
 		<a class="{{if .PageIsOrgSettingsLabels}}active{{end}} item" href="{{.OrgLink}}/settings/labels">
-			{{.i18n.Tr "repo.labels"}}
+			{{.locale.Tr "repo.labels"}}
 		</a>
 		<a class="{{if .PageIsSettingsDelete}}active{{end}} item" href="{{.OrgLink}}/settings/delete">
-			{{.i18n.Tr "org.settings.delete"}}
+			{{.locale.Tr "org.settings.delete"}}
 		</a>
 	</div>
 </div>