[auth][ios] Add app language constants

ios/RNFirebase/auth/RNFirebaseAuth.m

@@ -1166,6 +1166,25 @@ RCT_EXPORT_METHOD(useDeviceLanguage:
     return output;
 }
 
+/**
+ * React native constant exports - exports native firebase apps mainly
+ * @return NSDictionary
+ */
+- (NSDictionary *)constantsToExport {
+    NSMutableDictionary *constants = [NSMutableDictionary new];
+    NSDictionary *firApps = [FIRApp allApps];
+    NSMutableDictionary *appLanguage = [NSMutableDictionary new];
+
+    for (id key in firApps) {
+        FIRApp *firApp = firApps[key];
+
+        appLanguage[firApp.name] = [FIRAuth authWithApp:firApp].languageCode;
+    }
+
+    constants[@"APP_LANGUAGE"] = appLanguage;
+    return constants;
+}
+
 /**
  Converts a FIRUser instance into a dictionary to send via RNBridge