Detect Language of NSString

user_347741 0
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Somebody told me about a class for language recognition in Cocoa. Does anybody know which one it is?

This is not working:

NSSpellChecker *spellChecker = [NSSpellChecker sharedSpellChecker];
[spellChecker setAutomaticallyIdentifiesLanguages:YES];
NSString *spellCheckText = @"Guten Tag Herr Mustermann. Dies ist ein deutscher Text. Bitte löschen Sie diesen nicht.";
[spellChecker checkSpellingOfString:spellCheckText startingAt:0];
NSLog(@"%@", [spellChecker language]);

The result is 'en' but should be 'de'.

objective-c cocoa ios
6 Answers

With Swift 5, you can choose one of the following approaches in order to detect the language of a given string.

#1. Using NSLinguisticTagger's dominantLanguage property

Since iOS 11, NSLinguisticTagger has a property called dominantLanguage. dominantLanguage has the following declaration:

var dominantLanguage: String? { get }

Returns the dominant language of the string set for the linguistic tagger.

The Playground sample code below show how to use dominantLanguage in order to know the dominant language of a string:

import Foundation

let text = "あなたはそれを行うべきではありません。"
let tagger = NSLinguisticTagger(tagSchemes: [.language], options: 0)
tagger.string = text
let language = tagger.dominantLanguage
print(language) // Optional("ja")

#2. Using NSLinguisticTagger's dominantLanguage(for:) method

As an alternative, NSLinguisticTagger has a convenience method called dominantLanguage(for:) for creating a new linguistic tagger, setting its string property and getting the dominantLanguage property. dominantLanguage(for:) has the following declaration:

class func dominantLanguage(for string: String) -> String?

Returns the dominant language for the specified string.

Usage:

import Foundation

let text = "Die Kleinen haben friedlich zusammen gespielt."
let language = NSLinguisticTagger.dominantLanguage(for: text)
print(language) // Optional("de")

#3. Using NLLanguageRecognizer's dominantLanguage property

Since iOS 12, NLLanguageRecognizer has a property called dominantLanguage. dominantLanguage has the following declaration:

var dominantLanguage: NLLanguage? { get }

The most likely language for the processed text.

Here’s how to use dominantLanguage to guess the dominant language of natural language text:

import NaturalLanguage

let string = "J'ai deux amours. Mon pays et Paris."
let recognizer = NLLanguageRecognizer()
recognizer.processString(string)
let language = recognizer.dominantLanguage
print(language?.rawValue) // Optional("fr")
user_19661090

As of iOS 11 you can use the dominantLanguage(for:)/dominantLanguageForString: class method of NSLinguisticTagger.

Swift:

extension String {
    var language: String? {
        return NSLinguisticTagger.dominantLanguage(for: self)
    }
}

print("Good morning".language)
print("Buenos días".language)

Objective-C:

@interface NSString (Tagger)

@property (nonatomic, readonly, nullable) NSString *language;
@end

@implementation NSString (Tagger)

- (NSString *)language {
    return [NSLinguisticTagger dominantLanguageForString:self];
}

@end

NSLog(@"%@", @"Good morning".language);
NSLog(@"%@", @"Buenos días".language);

Output (for both):

en
es

user_12269630
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