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/explore/organizations.tmpl

@@ -12,7 +12,7 @@
 						<span class="header">
 							<a href="{{.HomeLink}}">{{.Name}}</a> {{.FullName}}
 							{{if .Visibility.IsPrivate}}
-								<span class="ui basic label">{{$.i18n.Tr "repo.desc.private"}}</span>
+								<span class="ui basic label">{{$.locale.Tr "repo.desc.private"}}</span>
 							{{end}}
 						</span>
 						<div class="description">
@@ -23,12 +23,12 @@
 								{{svg "octicon-link"}}
 								<a href="{{.Website}}" rel="nofollow">{{.Website}}</a>
 							{{end}}
-							{{svg "octicon-clock"}} {{$.i18n.Tr "user.join_on"}} {{.CreatedUnix.FormatShort}}
+							{{svg "octicon-clock"}} {{$.locale.Tr "user.join_on"}} {{.CreatedUnix.FormatShort}}
 						</div>
 					</div>
 				</div>
 			{{else}}
-				<div>{{$.i18n.Tr "explore.org_no_results"}}</div>
+				<div>{{$.locale.Tr "explore.org_no_results"}}</div>
 			{{end}}
 		</div>