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/user/settings/grants_oauth2.tmpl

@@ -1,10 +1,10 @@
 <h4 class="ui top attached header">
-	{{.i18n.Tr "settings.authorized_oauth2_applications"}}
+	{{.locale.Tr "settings.authorized_oauth2_applications"}}
 </h4>
 <div class="ui attached segment">
 	<div class="ui key list">
 		<div class="item">
-			{{.i18n.Tr "settings.authorized_oauth2_applications_description"}}
+			{{.locale.Tr "settings.authorized_oauth2_applications_description"}}
 		</div>
 		{{range $grant := .Grants}}
 			<div class="item">
@@ -12,7 +12,7 @@
 					<button class="ui red tiny button delete-button" data-modal-id="revoke-gitea-oauth2-grant"
 							data-url="{{AppSubUrl}}/user/settings/applications/oauth2/revoke"
 							data-id="{{$grant.ID}}">
-						{{$.i18n.Tr "settings.revoke_key"}}
+						{{$.locale.Tr "settings.revoke_key"}}
 					</button>
 				</div>
 				<div class="left floated content">
@@ -21,7 +21,7 @@
 				<div class="content">
 					<strong>{{$grant.Application.Name}}</strong>
 					<div class="activity meta">
-						<i>{{$.i18n.Tr "settings.add_on"}} <span>{{$grant.CreatedUnix.FormatShort}}</span></i>
+						<i>{{$.locale.Tr "settings.add_on"}} <span>{{$grant.CreatedUnix.FormatShort}}</span></i>
 					</div>
 				</div>
 			</div>
@@ -32,10 +32,10 @@
 <div class="ui small basic delete modal" id="revoke-gitea-oauth2-grant">
 	<div class="ui icon header">
 		{{svg "octicon-shield" 16 "mr-2"}}
-		{{.i18n.Tr "settings.revoke_oauth2_grant"}}
+		{{.locale.Tr "settings.revoke_oauth2_grant"}}
 	</div>
 	<div class="content">
-		<p>{{.i18n.Tr "settings.revoke_oauth2_grant_description"}}</p>
+		<p>{{.locale.Tr "settings.revoke_oauth2_grant_description"}}</p>
 	</div>
 	{{template "base/delete_modal_actions" .}}
 </div>