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Translate text with ML Kit on Android

You can use ML Kit to translate text between languages. ML Kit currently supports translation between 59 languages.

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

Before you begin

  1. If you haven't already, add Firebase to your Android project.
  2. In your project-level build.gradle file, make sure to include Google's Maven repository in both your buildscript and allprojects sections.
  3. Add the dependencies for the ML Kit Android libraries to your module (app-level) Gradle file (usually app/build.gradle):
    dependencies {
      // ...
    
      implementation 'com.google.firebase:firebase-ml-natural-language:21.0.3'
      implementation 'com.google.firebase:firebase-ml-natural-language-translate-model:20.0.6'
    }
    apply plugin: 'com.google.gms.google-services'
    

Translate a string of text

To translate a string between two languages:

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

    Java

    // Create an English-German translator:
    FirebaseTranslatorOptions options =
            new FirebaseTranslatorOptions.Builder()
                    .setSourceLanguage(FirebaseTranslateLanguage.EN)
                    .setTargetLanguage(FirebaseTranslateLanguage.DE)
                    .build();
    final FirebaseTranslator englishGermanTranslator =
            FirebaseNaturalLanguage.getInstance().getTranslator(options);
    

    Kotlin

    // Create an English-German translator:
    val options = FirebaseTranslatorOptions.Builder()
            .setSourceLanguage(FirebaseTranslateLanguage.EN)
            .setTargetLanguage(FirebaseTranslateLanguage.DE)
            .build()
    val englishGermanTranslator = FirebaseNaturalLanguage.getInstance().getTranslator(options)
    

    If you don't know the language of the input text, you can use the language identification API first. (But be sure you don't keep too many language models on the device at once.)

  2. Make sure the required translation model has been downloaded to the device. Don't call translate() until you know the model is available.

    Java

    FirebaseModelDownloadConditions conditions = new FirebaseModelDownloadConditions.Builder()
        .requireWifi()
        .build();
    englishGermanTranslator.downloadModelIfNeeded(conditions)
          .addOnSuccessListener(
              new OnSuccessListener<Void>() {
                @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.
                  // ...
                }
              });
    

    Kotlin

    englishGermanTranslator.downloadModelIfNeeded()
            .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.
                // ...
            }
    

    Language models are around 30MB, so don't download them unnecessarily, and only download them using WiFi, unless the user has specified otherwise. You should also delete unneeded models. See Explicitly manage translation models.

  3. After you confirm the model has been downloaded, pass a string of text in the source language to translate():

    Java

    englishGermanTranslator.translate(text)
          .addOnSuccessListener(
              new OnSuccessListener<String>() {
                @Override
                public void onSuccess(@NonNull String translatedText) {
                  // Translation successful.
                }
              })
          .addOnFailureListener(
              new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                  // Error.
                  // ...
                }
              });
    

    Kotlin

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

    The translated text, in the target language you configured, is passed to the success listener.

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.

Java

FirebaseTranslateModelManager modelManager = FirebaseTranslateModelManager.getInstance();

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

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

// Download the French model.
FirebaseModelDownloadConditions conditions = new FirebaseModelDownloadConditions.Builder()
        .requireWifi()
        .build();
FirebaseTranslateRemoteModel frModel =
        new FirebaseTranslateRemoteModel.Builder(FirebaseTranslateLanguage.FR)
                .setDownloadConditions(conditions)
                .build();
modelManager.downloadRemoteModelIfNeeded(frModel)
        .addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void v) {
                // Model downloaded.
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                // Error.
            }
        });

Kotlin

val modelManager = FirebaseTranslateModelManager.getInstance()

// Get translation models stored on the device.
modelManager.getAvailableModels(FirebaseApp.getInstance())
        .addOnSuccessListener { models ->
            // ...
        }
        .addOnFailureListener {
            // Error.
        }

// Delete the German model if it's on the device.
val deModel = FirebaseTranslateRemoteModel.Builder(FirebaseTranslateLanguage.DE).build()
modelManager.deleteDownloadedModel(deModel)
        .addOnSuccessListener {
            // Model deleted.
        }
        .addOnFailureListener {
            // Error.
        }

// Download the French model.
val conditions = FirebaseModelDownloadConditions.Builder()
        .requireWifi()
        .build()
val frModel = FirebaseTranslateRemoteModel.Builder(FirebaseTranslateLanguage.FR)
        .setDownloadConditions(conditions)
        .build()
modelManager.downloadRemoteModelIfNeeded(frModel)
        .addOnSuccessListener {
            // Model downloaded.
        }
        .addOnFailureListener {
            // Error.
        }