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Transifex iOS SDK

Transifex iOS SDK is a collection of tools to easily localize your iOS applications using Transifex Native.

The SDK can fetch translations over the air (OTA), manages an internal cache of translations and works seamlessly without requiring any changes in the source code of the app by the developer.

Both Objective-C and Swift projects are supported and iOS 10+ is required.

The package is built using Swift 5.3, as it currently requires a bundled resource to be present in the package (which was introduced on version 5.3). An update that will require a lower Swift version is currently WIP.

Learn more about Transifex Native.

The full SDK documentation is available at

Minimum Requirements

Swift Xcode Platforms
Swift 5.3 Xcode 12.3 iOS 10.0


The SDK allows you to keep using the same localization hooks that the iOS framework provides, such as NSLocalizedString, String.localizedStringWithFormat(format:...), etc, while at the same time taking advantage of the features that Transifex Native offers, such as OTA translations.

Below you can find examples of the SDK initialization both in Swift and Objective-C for an app that uses the English language (en) as its source locale and it's localized both in Greek (el) and French (fr).

Keep in mind that in the sample codes below you will have to replace <transifex_token> and <transifex_secret> with the actual token and secret that are associated with your Transifex project and resource.

SDK configuration (Swift)

To complete the setup you will need to:

Add "Transifex" as a package dependency in Xcode, by selecting your project, heading over to the 'Swift Packages' section, tapping on the '+' button, and entering the public repository URL in the search field. Initialize the SDK in your application using the transifex_token provided by your Transifex Native project.

Here is a basic configuration example in Swift:

import Transifex

class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
            locales: TXLocaleState(sourceLocale: "en",
                                   appLocales: ["en", "el", "fr"]),
            token: "<transifex_token>"

        return true

And a more complex one, defining a policy for handling missing translations and providing a secret for programmatically pushing strings.

import Transifex

class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
            locales: TXLocaleState(sourceLocale: "en",
                                   appLocales: ["en", "el", "fr"]),
            token: "<transifex_token>",
            secret: "<transifex_secret>",
            missingPolicy: TXCompositePolicy(
                TXWrappedStringPolicy(start: "[", end: "]")

        /// Optional: Fetch translations on launch
        return true

For Swift projects, you will also need to copy the TXNativeExtensions.swift file in your project and include it in all of the targets that call any of the following Swift methods:

  • String.localizedStringWithFormat(format:...)
  • NSString.localizedStringWithFormat(format:...)

If none of your application targets call any of the above methods, then you don't need to add this file to your project.

If you are interested in setting up the SDK for your application extensions as well, you can look into the related section in the documentation. The documentation also covers more special cases, such as providing a custom NSURLSession or configuring logging.

SDK configuration (Objective-C)

@import Transifex;

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    TXLocaleState *localeState = [[TXLocaleState alloc] initWithSourceLocale:@"en"
    TXPseudoTranslationPolicy *pseudoTranslationPolicy = [TXPseudoTranslationPolicy new];
    TXWrappedStringPolicy *wrappedStringPolicy = [[TXWrappedStringPolicy alloc] initWithStart:@"["
    TXCompositePolicy *compositePolicy = [[TXCompositePolicy alloc] init:@[

    [TXNative initializeWithLocales:localeState

    /// Optional: Fetch translations on launch
    [TXNative fetchTranslations:nil

    return YES;

Alternative initialization

If you want your application to make use of the default behavior, you can initialize the SDK using a simpler initilization method:


    locales: localeState,
    token: "<transifex_token>"


[TXNative initializeWithLocales:localeState

Fetching translations

As soon as fetchTranslations is called, the SDK will attempt to download the translations for all locales that are defined in the initialization of TXNative.

The fetchTranslations method in the above examples is called as soon as the application launches, but that's not required. Depending on the application, the developer might choose to call that method whenever it is most appropriate (for example, each time the application is brought to the foreground or when the internet connectivity is established).

Pushing source content programmatically

In order to push the source translations to CDS, you will first need to prepare an array of TXSourceString objects that will hold all the necessary information needed for CDS. You can refer to the TXSourceString class for more information, or you can look at the list below:

  • key (required): The key of the source string, generated via the public txGenerateKey() method.
  • sourceString (required): The actual source string.
  • developerComment (optional): An optional comment provided by the developer to assist the translators.
  • occurrences (required): A list of relative paths where the source string is located in the project.
  • tags (optional): An optional list of tags that will appear alongside the source string in the Transifex dashboard.
  • characterLimit (requred): Source string limit that should be respected by translators.
  • context (optional): An optional list of strings that provide more context.

After building an array of TXSourceString objects, use the pushTranslations method to push them to CDS. You can optionally set the purge argument to true (defaults to false) to replace the entire resource content. The completion handler can be used to get notified asynchronously whether the request was successful or not.

Pushing source content using the CLI

Use the Transifex CLI-swift to collect all your app content and send it to Transifex for translation. To perform this action you will need the transifex_secret token that you created in your Transifex Native project.

txios-cli push --token <transifex_token> --secret <transifex_secret> --project MyApp.xcodeproj

You may also use the --excluded-files option in the push command, providing a space separated list of filenames to be excluded from processing.


txios-cli push ... --excluded-files ExcludedFile1.strings ExcludedFile2.strings

For more details and additional options, please refer to the related Transifex CLI-swift documentation.

Display translated content

By default, the iOS Native SDK uses the current locale set on the iOS device and also listens for changes to the current locale.

Developers can override this setting by providing a custom class that conforms to the TXCurrentLocaleProvider protocol and returns a specific locale code in the currentLocale() method.

This custom locale provider can then be provided during the initialization of the TXLocaleState object as its final argument (currentLocaleProvider):

Swift example:

class CustomLocaleProvider : TXCurrentLocaleProvider {
    func currentLocale() -> String {
        return "el"

let locales = TXLocaleState(sourceLocale: "en",
                            appLocales: ["en", "el"],
                            currentLocaleProvider: CustomLocaleProvider())

TXNative.initialize(locales: locales,
                    token: "<token>")

Objective-C example:

@interface CustomLocaleProvider : NSObject <TXCurrentLocaleProvider>


@implementation CustomLocaleProvider

- (NSString *)currentLocale {
    return @"el";


/// ...

TXLocaleState *locales = [[TXLocaleState alloc] initWithSourceLocale:@"en"
                                                          appLocales:@[@"en", @"el"]

[TXNative initializeWithLocales:locales

It is worth noting that the iOS SDK manages an internal cache of translations in the file system of the translations fetched over-the-air.

You can find more about caching in the documentation.

Standard Cache

The default cache strategy used by the SDK, if no other cache is provided by the developer, is the TXStandardCache.getCache(). The standard cache operates by making use of the publicly exposed classes and protocols from the Cache.swift file of the SDK, so it's easy to construct another cache strategy if that's desired.

The standard cache is initialized with a memory cache (TXMemoryCache) that manages all cached entries in memory. After the memory cache gets initialized, it tries to look up if there are any already stored cache files in the file system using the TXDiskCacheProvider class:

  • The first cache provider is the bundle cache provider, that looks up for an already created cache file in the main application bundle of the app that may have been offered by the developer.
  • The second cache provider looks up for a cache file in the application sandbox directory (using the optional app group identifier argument if provided), in case the app had already downloaded the translations from the server from a previous launch.

Those two providers are used to initialize the memory cache using an update policy (TXCacheUpdatePolicy) which is optionally provided by the developer and defaults to the replaceAll value.

After the cached entries have updated the memory cache, the cache is ready to be used.

Whenever new translations are fetched from the server using the fetchTranslations() method, the standard cache is updated and those translations are stored as-is in the file system, in the same cache file used by the aforementioned second cache provider so that they are available on the next app launch.

Alternative cache strategy

You might want to update the internal memory cache as soon as the newly downloaded translations are available and always update all entries, so that the update policy can also be ommited.

In order to achieve that, you can create a new TXDecoratorCache subclass or create a method that returns a TXCache instance, just like in the TXStandardCache.getCache() case.

func getCustomCache() -> TXCache {
    return TXFileOutputCacheDecorator(
        fileURL: ...,
        internalCache: ...

This way, whenever the cache is updated with the new translations from the fetchTranslations() method, the update() call will propagate to the internal TXMemoryCache and update all of its entries.

Application Extensions

In order to add the SDK to an application extension target, be sure to include the Transifex library in the 'Frameworks and Libraries' section of the General settings of the application extension you are working on.

Furthermore, in case Xcode produces a "No such module 'Transifex'" error on the import Transifex statements of the extension files, be sure to add the $(SRCROOT) path in the 'Framework Search Paths' setting under the Build Settings of the application extension target.

In order to make the Transifex SDK cache file visible by both the extension and the main application targets, you would need to enable the App Groups capability in both the main application and the extension targets and use an existing or create a new app group identifier. Then, you would need to initialize the Transifex SDK with the TXStandardCache passing that app group identifier as the groupIdentifier argument.

URL Session

By default, an ephemeral URLSession object with no cache is used for all requests made to the CDS service.

For more control over the networking layer, an optional session parameter is exposed in the initialize() method of the TXNative cache, so that developers can offer their own session object, if that's desirable (e.g. for more fine grained cache control, certificate pinning etc).


By default, warning and error messages produced by the SDK are logged in the console using the print() method. Developers can offer a class that conforms to the TXLogger protocol so that they can control the logging mechanism of the SDK or make use of the public TXStandardLogHandler class to control the log level printed to the console.


Special cases

Localized strings that are being managed by the OS are not supported by the Transifex SDK:

  • Localized entries found in the Info.plist file (e.g. Bundle Display Name and Usage Description strings) that are included in the InfoPList.strings file.
  • Localized entried found in the Root.plist of the Settings.bundle of an app that exposes its Settings to the iOS Settings app that are included in the Root.strings file.


The SDK does not currently support SwiftUI views.

ICU support

Also, currently SDK supports only supports the platform rendering strategy, so if the ICU rendering strategy is passed during the initialization, translations will trigger the error policy.

Internet connectivity

If the device cannot access the Internet when fetchTranslations() method is called, the internal logic of the SDK doesn't retry or wait for a connection, in order to preserve resources. Developers are free to detect when internet connectivity is regained in order to re-call that method.

Sample applications

You can find two sample applications that make use of the Transifex iOS SDK, in Swift and Objective-C.


The documentation of this SDK has been generated using Jazzy using the following command:

jazzy -g -m Transifex


Licensed under Apache License 2.0, see LICENSE file.