app: Translate the "about" page button on popup menu

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/widgets/app.dart

@@ -323,14 +323,15 @@ class ChooseAccountPageOverflowButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final zulipLocalizations = ZulipLocalizations.of(context);
     final materialLocalizations = MaterialLocalizations.of(context);
     return MenuAnchor(
       menuChildren: [
         MenuItemButton(
           onPressed: () {
             Navigator.push(context, AboutZulipPage.buildRoute(context));
           },
-          child: const Text('About Zulip')), // TODO(i18n)
+          child: Text(zulipLocalizations.aboutPageTitle)),
       ],
       builder: (BuildContext context, MenuController controller, Widget? child) {
         return IconButton(