Wire up locale notifications to ios.

Fixes #2282

sky/shell/platform/ios/sky_surface.mm

@@ -157,6 +157,12 @@ static std::string TracesBasePath() {
            selector:@selector(keyboardWillBeHidden:)
                name:UIKeyboardWillHideNotification
              object:nil];
+
+    [[NSNotificationCenter defaultCenter]
+        addObserver:self
+           selector:@selector(onLocaleUpdated:)
+               name:NSCurrentLocaleDidChangeNotification
+             object:nil];
   }
   return self;
 }
@@ -179,6 +185,13 @@ static std::string TracesBasePath() {
   _engine->OnViewportMetricsChanged(_viewportMetrics.Clone());
 }
 
+- (void)onLocaleUpdated:(NSNotification*)notification {
+    NSLocale *currentLocale = [NSLocale currentLocale];
+    NSString *languageCode = [currentLocale objectForKey:NSLocaleLanguageCode];
+    NSString *countryCode = [currentLocale objectForKey:NSLocaleCountryCode];
+    _engine->OnLocaleChanged(languageCode.UTF8String, countryCode.UTF8String);
+}
+
 - (void)layoutSubviews {
   TRACE_EVENT0("flutter", "layoutSubviews");
   [super layoutSubviews];
@@ -253,6 +266,9 @@ static std::string TracesBasePath() {
   services->services_provided_by_embedder = service_provider.Pass();
   _engine->SetServices(services.Pass());
 
+  // Initialize to current locale
+  [self onLocaleUpdated:nil];
+
 #if TARGET_IPHONE_SIMULATOR
   [self runFromDartSource];
 #else