Drops

The top Android app for 2018, according to Google, is Drops, which teaches languages using lessons that are rapid-paced, visual and limited to 5 minutes per session.  Drops offers a free (I love free) tier for casual learners; 5 minutes of learning per day, with more than 1,700 words in 99 topics.  More dedicated language learners can subscribe for premium features to achieve faster progress with unlimited learning time.  Available for both Android and iOS devices.

It's fun, mildly addictive and now a daily habit of mine.

https://languagedrops.com