Build the basic RCTLocalizationProvider

Summary:
Changelog:
[Internal][Add] - Build the basic RCTLocalizationProvider

RCTLocalizationProvider is to enable the localization in fabric. But I'd start with internal apps now.

Reviewed By: PeteTheHeat

Differential Revision: D22704051

fbshipit-source-id: 845693a131c325f3c3d92b2ff491d5421966ad3e

React/Fabric/RCTLocalizationProvider.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <React/RCTDefines.h>
+#import <UIKit/UIKit.h>
+
+@protocol RCTLocalizationProtocol <NSObject>
+
+/*
+ Call for other apps to use their own translation functions
+ */
+- (NSString *)localizedString:(NSString *)oldString withDescription:(NSString *)description;
+
+@end
+
+/*
+ * It allows to set delegate for RCTLocalizationProvider so that we could ask APPs to do translations.
+ * It's an experimental feature.
+ */
+RCT_EXTERN void setLocalizationDelegate(id<RCTLocalizationProtocol> delegate);
+
+/*
+ * It allows apps to provide their translated language pack in case the cannot do translation reactively.
+ * It's an experimental feature.
+ */
+RCT_EXTERN void setLocalizationLanguagePack(NSDictionary<NSString *, NSString *> *pack);
+
+@interface RCTLocalizationProvider : NSObject
+
++ (NSString *)RCTLocalizedString:(NSString *)oldString withDescription:(NSString *)description;
+
+@end

React/Fabric/RCTLocalizationProvider.mm

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTLocalizationProvider.h"
+
+#import <Foundation/Foundation.h>
+
+static id<RCTLocalizationProtocol> _delegate = nil;
+static NSDictionary<NSString *, NSString *> *_languagePack = nil;
+
+void setLocalizationDelegate(id<RCTLocalizationProtocol> delegate)
+{
+  _delegate = delegate;
+}
+
+void setLocalizationLanguagePack(NSDictionary<NSString *, NSString *> *pack)
+{
+  _languagePack = pack;
+}
+
+@implementation RCTLocalizationProvider
+
++ (NSString *)RCTLocalizedString:(NSString *)oldString withDescription:(NSString *)description
+{
+  if (_delegate != nil) {
+    return [_delegate localizedString:oldString withDescription:description];
+  }
+
+  if (_languagePack != nil) {
+    return _languagePack[oldString];
+  }
+
+  return oldString;
+}
+
+@end