Just as many readers are swapping paperbacks for tablets, many language learners are trading in their textbooks for apps so they can study on the go.

One of the most popular language applications on the market is Duolingo, a program that "gamifies" learning by rewarding players with points and new levels after they memorize vocabulary words and grammar points.

The app, which has over 170 million users around the world, currently offers over 20 language courses, including Spanish, Vietnamese and Turkish. But Japanese had been notably missing until this week, when it was released on Friday by the Apple store for iOS.