Set of tools to simplify "on the fly" localization in iOS apps.





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Set of tools to simplify "on the fly" localization in iOS apps.


There is the "standard" way Apple of localizing iOS apps using NSLocalizedString. It's versatile enought and you should stick to it unless you have good reasons not to.

I reuse the same localization files in an iOS app, on a web site and, possibly, in an app made for another platform. Advantage of JSON there is that libraries for handling JSON are available for just about any modern platform.

As a side advantage, it is much easier to create tools which do not rely on localizers being proficient with escaping C strings or use translation services not geared towards iOS app localization.

File format

MCLocalization uses strings files in JSON format. Internally, it is a collection of collections of strings. Here's an example from the sample project:

    "en": {
        "greeting": "Hello!",
        "message": "Tap on the buttons below to switch languages",
        "glory": "Glory Glory, %name%!",
        "mustache": "mustache",
        "lovely-mustache": "What a wonderful {{mustache}} you have!"
    "ru": {
        "greeting": "Привет!",
        "message": "Нажимайте на кнопки для смены языка",
        "glory": "Славься славься, %name%!",
        "mustache": "усы",
        "lovely-mustache": "Какие замечательные у Вас {{mustache}}!"

In case of using multiple JSON files, one for each individual language, file should contain strings for only that language:

    "greeting": "Hello!",
    "message": "Tap on the buttons below to switch languages",
    "glory": "Glory Glory, %name%!",
    "mustache": "mustache",
    "lovely-mustache": "What a wonderful {{mustache}} you have!"

Collection of strings for each language is referenced by a canonicalized IETF BCP 47 language identifier (the same identifier used in NSLocale). Strings in a collection are further identified by keys.


Add files from the 'Classes' folder to your project.


Initialize localization by loading strings:

Using a single JSON file:

[MCLocalization loadFromURL:[[NSBundle mainBundle] URLForResource:@"strings.json" withExtension:nil] defaultLanguage:@"en"];

Using multiple JSON files, one for each language:

NSDictionary * languageURLPairs = @{
    @"en":[[NSBundle mainBundle] URLForResource:@"en.json" withExtension:nil],
    @"ru":[[NSBundle mainBundle] URLForResource:@"ru.json" withExtension:nil],
[MCLocalization loadFromLanguageURLPairs:languageURLPairs defaultLanguage:@"en"];

Legacy way using a file path:

NSString * path = [[NSBundle mainBundle] pathForResource:@"strings.json" ofType:nil];
[MCLocalization loadFromJSONFile:path defaultLanguage:@"en"];

MCLocalization will try to determine the best mathing language based on device's language preferences, defaultLanguage prameter is a "fall-through" setting in case there is no match.

Here's how you fetch a localized string:

_label.text = [MCLocalization stringForKey:@"greeting"];

Here is how you use placeholders:

// Given the "key": "%a% {{b}} [c]", the following call will return "A B C"
[MCLocalization stringForKey:@"key" withPlaceholders:@{@"%a%":@"A", @"{{b}}":@"B"}, @"[c]":@"C"];

MCLocalization was designed to aid "instant" localization so that app's UI could update right after user updates the language setting. To update the localization language, set it like this:

[MCLocalization sharedInstance].language = @"ru";

Localization language will be set and a MCLocalizationLanguageDidChangeNotification notification will be send. This setting is stored in user defaults and next time app is launched, this setting will be used.

For using MCLocalization, I recommend this pattern:

Load localization strings in AppDelegate application:didFinishLaunchingWithOptions::

NSString * path = [[NSBundle mainBundle] pathForResource:@"strings.json" ofType:nil];
[MCLocalization loadFromJSONFile:path defaultLanguage:@"en"];

In UIViewController you want to localize, collect all the localization code in a dedicated function:

- (void)localize
    _greetingLabel.text = [MCLocalization stringForKey:@"greeting"];
    _messageLabel.text = [MCLocalization stringForKey:@"message"];
    _labelPlaceholders.text = [MCLocalization stringForKey:@"glory" withPlaceholders:@{@"%name%":@"Man United"}];
    _mustacheLabel.text = [MCLocalization stringForKey:@"lovely-mustache" withPlaceholders:@{@"{{mustache}}":[MCLocalization stringForKey:@"mustache"]}];

Call that function from the viewDidLoad and add view controller as an observer for the MCLocalizationLanguageDidChangeNotification:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(localize) name:MCLocalizationLanguageDidChangeNotification object:nil];
[self localize];

Handling missing localization

By default, localized string for a missing key will be nil. noKeyPlaceholder text can be set instead:

[MCLocalization sharedInstance].noKeyPlaceholder = @"[No '{key}' in '{language}']";

{key} and {language} placeholders will be replaced with corresponding settings.


Code in this project is available under the MIT license.

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