Adds a11y section locale support for iOS (#175005)

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part of flutter/flutter#99600

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Author: chunhtai

engine/src/flutter/shell/platform/darwin/ios/framework/Source/SemanticsObject.mm

@@ -454,6 +454,17 @@ - (BOOL)isAccessibilityElement {
   return [self isFocusable];
 }
 
+- (NSString*)accessibilityLanguage {
+  if (![self isAccessibilityBridgeAlive]) {
+    return nil;
+  }
+
+  if (self.node.locale.empty()) {
+    return nil;
+  }
+  return @(self.node.locale.data());
+}
+
 - (bool)isFocusable {
   // If the node is scrollable AND hidden OR
   // The node has a label, value, or hint OR

engine/src/flutter/shell/platform/darwin/ios/framework/Source/SemanticsObjectTest.mm

@@ -571,6 +571,33 @@ - (void)testFlutterSemanticsObjectHasIdentifier {
   XCTAssertTrue([object.accessibilityIdentifier isEqualToString:@"identifier"]);
 }
 
+- (void)testFlutterSemanticsObjectHasLocale {
+  flutter::testing::MockAccessibilityBridge* mock = new flutter::testing::MockAccessibilityBridge();
+  mock->isVoiceOverRunningValue = true;
+  fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(mock);
+  fml::WeakPtr<flutter::AccessibilityBridgeIos> bridge = factory.GetWeakPtr();
+
+  flutter::SemanticsNode node;
+  node.locale = "es-MX";
+
+  FlutterSemanticsObject* object = [[FlutterSemanticsObject alloc] initWithBridge:bridge uid:0];
+  [object setSemanticsNode:&node];
+  XCTAssertTrue([object.accessibilityLanguage isEqualToString:@"es-MX"]);
+}
+
+- (void)testFlutterSemanticsObjectLocaleNil {
+  flutter::testing::MockAccessibilityBridge* mock = new flutter::testing::MockAccessibilityBridge();
+  mock->isVoiceOverRunningValue = true;
+  fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(mock);
+  fml::WeakPtr<flutter::AccessibilityBridgeIos> bridge = factory.GetWeakPtr();
+
+  flutter::SemanticsNode node;
+
+  FlutterSemanticsObject* object = [[FlutterSemanticsObject alloc] initWithBridge:bridge uid:0];
+  [object setSemanticsNode:&node];
+  XCTAssertTrue(object.accessibilityLanguage == nil);
+}
+
 - (void)testFlutterScrollableSemanticsObjectWithLabelValueHintIsNotHiddenWhenVoiceOverIsRunning {
   flutter::testing::MockAccessibilityBridge* mock = new flutter::testing::MockAccessibilityBridge();
   mock->isVoiceOverRunningValue = true;