Identify the language of text with ML Kit on iOS

You can use ML Kit to identify the language of a string of text. You can get the string's most likely language or get confidence scores for all of the string's possible languages.

ML Kit recognizes text in 103 different languages in their native scripts. In addition, romanized text can be recognized for Arabic, Bulgarian, Chinese, Greek, Hindi, Japanese, and Russian.

Before you begin

  1. If you have not already added Firebase to your app, do so by following the steps in the getting started guide.
  2. Include the ML Kit libraries in your Podfile: 
    pod 'Firebase/MLNaturalLanguage', '6.25.0'
pod 'Firebase/MLNLLanguageID', '6.25.0'
    After you install or update your project's Pods, be sure to open your Xcode project using its .xcworkspace.
  3. In your app, import Firebase:

    Swift

    import Firebase

    Objective-C

    @import Firebase;

Identify the language of a string

To identify the language of a string, get an instance of LanguageIdentification, and then pass the string to the identifyLanguage(for:) method.

For example:

Swift

let languageId = NaturalLanguage.naturalLanguage().languageIdentification()

languageId.identifyLanguage(for: text) { (languageCode, error) in
  if let error = error {
    print("Failed with error: \(error)")
    return
  }
  if let languageCode = languageCode, languageCode != "und" {
    print("Identified Language: \(languageCode)")
  } else {
    print("No language was identified")
  }
}

Objective-C

FIRNaturalLanguage *naturalLanguage = [FIRNaturalLanguage naturalLanguage];
FIRLanguageIdentification *languageId = [naturalLanguage languageIdentification];

[languageId identifyLanguageForText:text
                         completion:^(NSString * _Nullable languageCode,
                                      NSError * _Nullable error) {
                           if (error != nil) {
                             NSLog(@"Failed with error: %@", error.localizedDescription);
                             return;
                           }
                           if (languageCode != nil
                               && ![languageCode isEqualToString:@"und"] ) {
                             NSLog(@"Identified Language: %@", languageCode);
                           } else {
                             NSLog(@"No language was identified");
                           }
                         }];

If the call succeeds, a BCP-47 language code is passed to the completion handler, indicating the language of the text. See the complete list of supported languages. If no language could be confidently detected, the code und (undetermined) is passed.

By default, ML Kit returns a non-und value only when it identifies the language with a confidence value of at least 0.5. You can change this threshold by passing a LanguageIdentificationOptions object to languageIdentification(options:):

Swift

let options = LanguageIdentificationOptions(confidenceThreshold: 0.4)
let languageId = NaturalLanguage.naturalLanguage().languageIdentification(options: options)

Objective-C

FIRNaturalLanguage *naturalLanguage = [FIRNaturalLanguage naturalLanguage];
FIRLanguageIdentificationOptions *options =
    [[FIRLanguageIdentificationOptions alloc] initWithConfidenceThreshold:0.4];
FIRLanguageIdentification *languageId =
    [naturalLanguage languageIdentificationWithOptions:options];

Get the possible languages of a string

To get the confidence values of a string's most likely languages, get an instance of LanguageIdentification, and then pass the string to the identifyPossibleLanguages(for:) method.

For example:

Swift

let languageId = NaturalLanguage.naturalLanguage().languageIdentification()

languageId.identifyPossibleLanguages(for: text) { (identifiedLanguages, error) in
  if let error = error {
    print("Failed with error: \(error)")
    return
  }
  guard let identifiedLanguages = identifiedLanguages,
    !identifiedLanguages.isEmpty,
    identifiedLanguages[0].languageCode != "und"
  else {
    print("No language was identified")
    return
  }

  print("Identified Languages:\n" +
    identifiedLanguages.map {
      String(format: "(%@, %.2f)", $0.languageCode, $0.confidence)
      }.joined(separator: "\n"))
}

Objective-C

FIRNaturalLanguage *naturalLanguage = [FIRNaturalLanguage naturalLanguage];
FIRLanguageIdentification *languageId = [naturalLanguage languageIdentification];

[languageId identifyPossibleLanguagesForText:text
                                  completion:^(NSArray<FIRIdentifiedLanguage *> * _Nonnull identifiedLanguages,
                                               NSError * _Nullable error) {
  if (error != nil) {
    NSLog(@"Failed with error: %@", error.localizedDescription);
    return;
  }
  if (identifiedLanguages.count == 1
      && [identifiedLanguages[0].languageCode isEqualToString:@"und"] ) {
    NSLog(@"No language was identified");
    return;
  }
  NSMutableString *outputText = [NSMutableString stringWithFormat:@"Identified Languages:"];
  for (FIRIdentifiedLanguage *language in identifiedLanguages) {
    [outputText appendFormat:@"\n(%@, %.2f)", language.languageCode, language.confidence];
  }
  NSLog(outputText);
}];

If the call succeeds, a list of IdentifiedLanguage objects is passed to the continuation handler. From each object, you can get the language's BCP-47 code and the confidence that the string is in that language. See the complete list of supported languages. Note that these values indicate the confidence that the entire string is in the given language; ML Kit doesn't identify multiple languages in a single string.

By default, ML Kit returns only languages with confidence values of at least 0.01. You can change this threshold by passing a LanguageIdentificationOptions object to languageIdentification(options:):

Swift

let options = LanguageIdentificationOptions(confidenceThreshold: 0.4)
let languageId = NaturalLanguage.naturalLanguage().languageIdentification(options: options)

Objective-C

FIRNaturalLanguage *naturalLanguage = [FIRNaturalLanguage naturalLanguage];
FIRLanguageIdentificationOptions *options =
    [[FIRLanguageIdentificationOptions alloc] initWithConfidenceThreshold:0.4];
FIRLanguageIdentification *languageId =
    [naturalLanguage languageIdentificationWithOptions:options];

If no language meets this threshold, the list will have one item, with the value und.