Translate text with ML Kit on Android

You can use ML Kit to translate text between languages. ML Kit can translation between more than 50 languages.

See the ML Kit quickstart sample on GitHub for an example of this API in use.

Before you begin

  1. In your project-level build.gradle file, make sure to include Google's Maven repository in both your buildscript and allprojects sections.
  2. Add the dependencies for the ML Kit Android libraries to your module's app-level gradle file, which is usually app/build.gradle:
    dependencies {
      // ...
    
      implementation 'com.google.mlkit:translate:16.1.1'
    }
    

Translate a string of text

To translate a string between two languages:

  1. Create a Translator object, configuring it with the source and target languages:

Kotlin

// Create an English-German translator:
val options = TranslatorOptions.Builder()
    .setSourceLanguage(TranslateLanguage.ENGLISH)
    .setTargetLanguage(TranslateLanguage.GERMAN)
    .build()
val englishGermanTranslator = Translator.getClient(options)

Java

// Create an English-German translator:
TranslatorOptions options =
    new TranslatorOptions.Builder()
        .setSourceLanguage(TranslateLanguage.ENGLISH)
        .setTargetLanguage(TranslateLanguage.GERMAN)
        .build();
final Translator englishGermanTranslator =
    Translation.getClient(options);
If you don't know the language of the input text, you can use the [Language
Identification API](/ml-kit/languages/identification) which
gives you a language tag. Then convert the tag to a `TranslateLanguage`
using [`TranslateLanguage.fromLanguageTag()`]().

Avoid keeping too many language models on the device at once.
  1. Make sure the required translation model has been downloaded to the device. Don't call translate() until you know the model is available.

Kotlin

var conditions = DownloadConditions.Builder()
    .requireWifi()
    .build()
englishGermanTranslator.downloadModelIfNeeded(conditions)
    .addOnSuccessListener {
        // Model downloaded successfully. Okay to start translating.
        // (Set a flag, unhide the translation UI, etc.)
    }
    .addOnFailureListener { exception ->
        // Model couldn’t be downloaded or other internal error.
        // ...
    }

Java

DownloadConditions conditions = new DownloadConditions.Builder()
    .requireWifi()
    .build();
englishGermanTranslator.downloadModelIfNeeded(conditions)
    .addOnSuccessListener(
        new OnSuccessListener() {
          @Override
          public void onSuccess(Void v) {
            // Model downloaded successfully. Okay to start translating.
            // (Set a flag, unhide the translation UI, etc.)
          }
        })
    .addOnFailureListener(
        new OnFailureListener() {
          @Override
          public void onFailure(@NonNull Exception e) {
            // Model couldn’t be downloaded or other internal error.
            // ...
          }
        });
Language models are around 30MB, so don't download them unnecessarily, and
only download them using Wi-Fi unless the user has specified otherwise. You
should also delete unneeded models.
See [Explicitly manage translation models](#manage-models).
  1. After you confirm the model has been downloaded, pass a string of text in the source language to translate():

Kotlin

englishGermanTranslator.translate(text)
    .addOnSuccessListener { translatedText ->
        // Translation successful.
    }
    .addOnFailureListener { exception ->
         // Error.
         // ...
    }

Java

englishGermanTranslator.translate(text)
    .addOnSuccessListener(
        new OnSuccessListener() {
          @Override
          public void onSuccess(@NonNull String translatedText) {
            // Translation successful.
          }
        })
    .addOnFailureListener(
        new OnFailureListener() {
          @Override
          public void onFailure(@NonNull Exception e) {
            // Error.
            // ...
          }
        });
The translated text, in the target language you configured, is passed to the
success listener.
  1. Ensure that the close() method is called when the Translator object will no longer be used.

    If you are using a Translator in a Fragment or AppCompatActivity, one easy way to do that is call LifecycleOwner.getLifecycle() on the Fragment or AppCompatActivity, and then call Lifecycle.addObserver. For example:

Kotlin

val options = ...
val translator = Translation.getClient(options)
getLifecycle().addObserver(translator)

Java

TranslatorOptions options = ...
Translator translator = Translation.getClient(options);
getLifecycle().addObserver(translator);
... use translator ...
Note that this assumes that the code is inside of a class that implements LifecycleOwner (e.g. a Fragment or AppCompatActivity).

Explicitly manage translation models

When you use the translation API as described above, ML Kit automatically downloads language-specific translation models to the device as required. You can also explicitly manage the translation models you want available on the device by using ML Kit's translation model management API. This can be useful if you want to download models ahead of time, or delete unneeded models from the device.

Kotlin

val modelManager = RemoteModelManager.getInstance()

// Get translation models stored on the device.
modelManager.getDownloadedModels(TranslateRemoteModel::class.java)
    .addOnSuccessListener { models ->
        // ...
    }
    .addOnFailureListener {
        // Error.
    }

// Delete the German model if it's on the device.
val germanModel = TranslateRemoteModel.Builder(TranslateLanguage.GERMAN).build()
modelManager.deleteDownloadedModel(germanModel)
    .addOnSuccessListener {
        // Model deleted.
    }
    .addOnFailureListener {
        // Error.
    }

// Download the French model.
val frenchModel = TranslateRemoteModel.Builder(TranslateLanguage.FRENCH).build()
val conditions = DownloadConditions.Builder()
    .requireWifi()
    .build()
modelManager.download(frenchModel, conditions)
    .addOnSuccessListener {
        // Model downloaded.
    }
    .addOnFailureListener {
        // Error.
    }

Java

RemoteModelManager modelManager = RemoteModelManager.getInstance();

// Get translation models stored on the device.
modelManager.getDownloadedModels(TranslateRemoteModel.class)
    .addOnSuccessListener(new OnSuccessListener>() {
        @Override
        public void onSuccess(Set models) {
            // ...
        }
    })
    .addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            // Error.
        }
    });

// Delete the German model if it's on the device.
TranslateRemoteModel germanModel =
        new TranslateRemoteModel.Builder(TranslateLanguage.GERMAN).build();
modelManager.deleteDownloadedModel(germanModel)
    .addOnSuccessListener(new OnSuccessListener() {
        @Override
        public void onSuccess(Void v) {
            // Model deleted.
        }
    })
    .addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            // Error.
        }
    });

// Download the French model.
TranslateRemoteModel frenchModel =
        new TranslateRemoteModel.Builder(TranslateLanguage.FRENCH).build();
DownloadConditions conditions = new DownloadConditions.Builder()
    .requireWifi()
    .build();
modelManager.download(frenchModel, conditions)
    .addOnSuccessListener(new OnSuccessListener() {
        @Override
        public void onSuccess(Void v) {
            // Model downloaded.
        }
    })
    .addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            // Error.
        }
    });