Add localization for Back and Cancel buttons in CupertinoNavigationBar (#162581)

### Description
This PR adds localization support for the **"Back"** and **"Cancel"**
buttons used in `CupertinoNavigationBar`.

#### Changes:  
- Introduced `cancelButtonLabel` and `backButtonLabel` in
`CupertinoLocalizations`.
- ~Updated all ARB files with appropriate translations.~  
- Modified `_NavigationBarStaticComponents` and `_BackLabel` to use
these labels.
- Ensured all localization tests pass.
- Fixed the test `Auto back/close button` in the
`packages/flutter/test/cupertino/localizations_test.dart`.

### Why is this needed?
Currently, the **"Back"** and **"Cancel"** (prev. **"Close"**) buttons
in `CupertinoNavigationBar` are hardcoded in English. This update
ensures they are properly localized across supported languages.

### Tests
One test failed (even before my changes): `Saturation is applied before
blur`
![Screenshot from 2025-02-02
17-02-20](https://github.com/user-attachments/assets/466df00a-6c28-4bb4-959b-9eee5533d5e3)

#### Manual Testing with the `modal_bottom_sheet` Package

I tested the change using [my custom mini
app](https://gist.github.com/Michae1Weiss/9afee8c425d03e3d41e331fdbf21344f)
and the `modal_bottom_sheet` package. I verified that the button is
correctly translated into German localization.

##### Before

![cupertino_modal_cancel_button_before_change](https://github.com/user-attachments/assets/7bb41909-43c8-4ece-a885-b17c24193b51)

##### After

![cupertino_modal_cancel_button_after_change](https://github.com/user-attachments/assets/bf5f8904-71e8-4b39-8cee-8c8eb8de7c77)

### Button Name Change: From "Close" to "Cancel"

I have renamed the button from **"Close"** to **"Cancel"** to align with
the iOS native naming convention for buttons in modal dialogs.
  
#### Example:

![cancel_button](https://github.com/user-attachments/assets/32d3ac7e-8d18-4ba0-b13d-aa54f61a476a)


### Related Issues
[CupertinoNavigationBar's "Close", "Back", and "Cancel" buttons are not
localized. **#48616** ](flutter/flutter#48616)
[CupertinoNavigationBar's "Back" button is not localized **#120722**
](flutter/flutter#120722)

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [X] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [X] I signed the [CLA].
- [X] I listed at least one issue that this PR fixes in the description
above.
- [X] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [X] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [X] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

Author: Michae1Weiss

packages/flutter/lib/src/cupertino/localizations.dart

@@ -302,6 +302,12 @@ abstract class CupertinoLocalizations {
   /// indicate that a tap outside dismisses the context menu.
   String get menuDismissLabel;
 
+  /// The label for the cancel button in modal views, used in [CupertinoNavigationBar] and [CupertinoSliverNavigationBar].
+  String get cancelButtonLabel;
+
+  /// The label for the back button, used in [CupertinoNavigationBar] and [CupertinoSliverNavigationBar].
+  String get backButtonLabel;
+
   /// The `CupertinoLocalizations` from the closest [Localizations] instance
   /// that encloses the given context.
   ///
@@ -520,6 +526,12 @@ class DefaultCupertinoLocalizations implements CupertinoLocalizations {
   @override
   String get menuDismissLabel => 'Dismiss menu';
 
+  @override
+  String get cancelButtonLabel => 'Cancel';
+
+  @override
+  String get backButtonLabel => 'Back';
+
   /// Creates an object that provides US English resource values for the
   /// cupertino library widgets.
   ///

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -17,6 +17,7 @@ import 'button.dart';
 import 'colors.dart';
 import 'constants.dart';
 import 'icons.dart';
+import 'localizations.dart';
 import 'page_scaffold.dart';
 import 'route.dart';
 import 'search_field.dart';
@@ -241,7 +242,7 @@ bool _isTransitionable(BuildContext context) {
 /// toolbar, typically for actions and navigation.
 ///
 /// The [leading] widget will automatically be a back chevron icon button (or a
-/// close button in case of a fullscreen dialog) to pop the current route if none
+/// cancel button in case of a fullscreen dialog) to pop the current route if none
 /// is provided and [automaticallyImplyLeading] is true (true by default).
 ///
 /// This toolbar should be placed at top of the screen where it will
@@ -412,7 +413,7 @@ class CupertinoNavigationBar extends StatefulWidget implements ObstructingPrefer
   ///
   /// Specifically this navigation bar will:
   ///
-  /// 1. Show a 'Close' button if the current route is a `fullscreenDialog`.
+  /// 1. Show a 'Cancel' button if the current route is a `fullscreenDialog`.
   /// 2. Show a back chevron with [previousPageTitle] if [previousPageTitle] is
   ///    not null.
   /// 3. Show a back chevron with the previous route's `title` if the current
@@ -729,6 +730,7 @@ class _CupertinoNavigationBarState extends State<CupertinoNavigationBar> {
       userLargeTitle: widget.largeTitle,
       large: widget.largeTitle != null,
       staticBar: true, // This one does not scroll
+      context: context,
     );
 
     // Standard persistent components
@@ -840,7 +842,7 @@ class _CupertinoNavigationBarState extends State<CupertinoNavigationBar> {
 /// widget on the static section on top that remains while scrolling.
 ///
 /// The [leading] widget will automatically be a back chevron icon button (or a
-/// close button in case of a fullscreen dialog) to pop the current route if none
+/// cancel button in case of a fullscreen dialog) to pop the current route if none
 /// is provided and [automaticallyImplyLeading] is true (true by default).
 ///
 /// The [largeTitle] widget will automatically be a title text from the current
@@ -1266,6 +1268,7 @@ class _CupertinoSliverNavigationBarState extends State<CupertinoSliverNavigation
       padding: widget.padding,
       large: true,
       staticBar: false, // This one scrolls.
+      context: context,
     );
 
     return MediaQuery.withNoTextScaling(
@@ -1802,12 +1805,14 @@ class _NavigationBarStaticComponents {
     required EdgeInsetsDirectional? padding,
     required bool large,
     required bool staticBar,
+    required BuildContext context,
   }) : leading = createLeading(
          leadingKey: keys.leadingKey,
          userLeading: userLeading,
          route: route,
          automaticallyImplyLeading: automaticallyImplyLeading,
          padding: padding,
+         context: context,
        ),
        backChevron = createBackChevron(
          backChevronKey: keys.backChevronKey,
@@ -1865,6 +1870,7 @@ class _NavigationBarStaticComponents {
     required ModalRoute<dynamic>? route,
     required bool automaticallyImplyLeading,
     required EdgeInsetsDirectional? padding,
+    required BuildContext context,
   }) {
     Widget? leadingContent;
 
@@ -1879,7 +1885,7 @@ class _NavigationBarStaticComponents {
         onPressed: () {
           route.navigator!.maybePop();
         },
-        child: const Text('Close'),
+        child: Text(CupertinoLocalizations.of(context).cancelButtonLabel),
       );
     }
 
@@ -2094,12 +2100,13 @@ class CupertinoNavigationBarBackButton extends StatelessWidget {
       );
     }
 
+    final CupertinoLocalizations localizations = CupertinoLocalizations.of(context);
     return CupertinoButton(
       padding: EdgeInsets.zero,
       child: Semantics(
         container: true,
         excludeSemantics: true,
-        label: 'Back',
+        label: localizations.backButtonLabel,
         button: true,
         child: DefaultTextStyle(
           style: actionTextStyle,
@@ -2191,7 +2198,7 @@ class _BackLabel extends StatelessWidget {
     Text textWidget = Text(previousTitle, maxLines: 1, overflow: TextOverflow.ellipsis);
 
     if (previousTitle.length > 12) {
-      textWidget = const Text('Back');
+      textWidget = Text(CupertinoLocalizations.of(context).backButtonLabel);
     }
 
     return Align(alignment: AlignmentDirectional.centerStart, widthFactor: 1.0, child: textWidget);
@@ -2227,16 +2234,15 @@ class _CancelButton extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final CupertinoLocalizations localizations = CupertinoLocalizations.of(context);
     return Align(
       alignment: Alignment.centerLeft,
       child: Opacity(
         opacity: opacity,
         child: CupertinoButton(
           padding: EdgeInsets.zero,
           onPressed: onPressed,
-          // TODO(victorsanni): Localize this string.
-          // See https://github.com/flutter/flutter/issues/48616.
-          child: const Text('Cancel', maxLines: 1, overflow: TextOverflow.clip),
+          child: Text(localizations.cancelButtonLabel, maxLines: 1, overflow: TextOverflow.clip),
         ),
       ),
     );

packages/flutter/test/cupertino/localizations_test.dart

@@ -37,6 +37,8 @@ void main() {
     expect(localizations.searchTextFieldPlaceholderLabel, isNotNull);
     expect(localizations.noSpellCheckReplacementsLabel, isNotNull);
     expect(localizations.clearButtonLabel, isNotNull);
+    expect(localizations.cancelButtonLabel, isNotNull);
+    expect(localizations.backButtonLabel, isNotNull);
   });
 
   testWidgets('CupertinoLocalizations.of throws', (WidgetTester tester) async {

packages/flutter/test/cupertino/nav_bar_test.dart

@@ -739,7 +739,7 @@ void main() {
     expect(tester.getBottomLeft(find.text('Title')).dy, 44.0); // Extension gone.
   });
 
-  testWidgets('Auto back/close button', (WidgetTester tester) async {
+  testWidgets('Auto back/cancel button', (WidgetTester tester) async {
     await tester.pumpWidget(
       const CupertinoApp(home: CupertinoNavigationBar(middle: Text('Home page'))),
     );
@@ -776,10 +776,10 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(milliseconds: 600));
 
-    expect(find.widgetWithText(CupertinoButton, 'Close'), findsOneWidget);
+    expect(find.widgetWithText(CupertinoButton, 'Cancel'), findsOneWidget);
 
     // Test popping goes back correctly.
-    await tester.tap(find.text('Close'));
+    await tester.tap(find.text('Cancel'));
 
     await tester.pump();
     await tester.pump(const Duration(milliseconds: 600));

packages/flutter_localizations/lib/src/l10n/cupertino_af.arb

@@ -27,5 +27,7 @@
   "lookUpButtonLabel": "Kyk op",
   "searchWebButtonLabel": "Deursoek web",
   "shareButtonLabel": "Deel …",
-  "clearButtonLabel": "Vee uit"
+  "clearButtonLabel": "Vee uit",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }

packages/flutter_localizations/lib/src/l10n/cupertino_am.arb

@@ -27,5 +27,7 @@
   "lookUpButtonLabel": "ይመልከቱ",
   "searchWebButtonLabel": "ድርን ፈልግ",
   "shareButtonLabel": "አጋራ...",
-  "clearButtonLabel": "አጽዳ"
+  "clearButtonLabel": "አጽዳ",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }

packages/flutter_localizations/lib/src/l10n/cupertino_ar.arb

@@ -47,5 +47,7 @@
   "menuDismissLabel": "إغلاق القائمة",
   "lookUpButtonLabel": "بحث عام",
   "searchWebButtonLabel": "البحث على الويب",
-  "shareButtonLabel": "مشاركة…"
+  "shareButtonLabel": "مشاركة…",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }

packages/flutter_localizations/lib/src/l10n/cupertino_as.arb

@@ -27,5 +27,7 @@
   "menuDismissLabel": "অগ্ৰাহ্য কৰাৰ মেনু",
   "lookUpButtonLabel": "ওপৰলৈ চাওক",
   "searchWebButtonLabel": "ৱেবত সন্ধান কৰক",
-  "shareButtonLabel": "শ্বেয়াৰ কৰক…"
+  "shareButtonLabel": "শ্বেয়াৰ কৰক…",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }

packages/flutter_localizations/lib/src/l10n/cupertino_az.arb

@@ -27,5 +27,7 @@
   "menuDismissLabel": "Menyunu qapadın",
   "lookUpButtonLabel": "Axtarın",
   "searchWebButtonLabel": "Vebdə axtarın",
-  "shareButtonLabel": "Paylaşın..."
+  "shareButtonLabel": "Paylaşın...",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }

packages/flutter_localizations/lib/src/l10n/cupertino_be.arb

@@ -37,5 +37,7 @@
   "menuDismissLabel": "Закрыць меню",
   "lookUpButtonLabel": "Знайсці",
   "searchWebButtonLabel": "Пошук у сетцы",
-  "shareButtonLabel": "Абагуліць..."
+  "shareButtonLabel": "Абагуліць...",
+  "cancelButtonLabel": "Cancel",
+  "backButtonLabel": "Back"
 }