How to detect the dominant language of a text string

Swift version: 5.1

Paul Hudson @twostraws May 28th 2019

The NSLinguisticTagger class has dedicated code to help you identify the dominant language of a text string. Before I show you the code, there are three important provisos:

It detects the dominant language, which means if you provide it with text that contains more than one language it will return whichever one appears most often.
If you give it text where no identification can be made, e.g. some numbers or an empty string, it will return nil.
It is extraordinarily fast – you can feed it thousands of article-length strings a second and it will fly through them.

Here’s an example to help you get started:

let text = "Ceci n'est pas une pipe"

if let language = NSLinguisticTagger.dominantLanguage(for: text) {
    print(language)
} else {
    print("Unknown language")
}

When that code runs it will print “fr”, because the dominant language in the text is French.