If you have previous experience with a language and feel that lessons are too easy, there are several ways to advance more quickly, skipping ahead by unlocking grayed out skills and lessons.
1. Take a placement test. This option is available the first time you start a new language to make sure you are placed in a spot that isn't too easy for you.
2. If you have previous experience with a language and feel that lessons are too easy, you can scroll to the next locked unit and tap the circle that says “Jump here?”. If you pass the test, you’ll unlock that unit!
NOTE: This will complete all levels up to that point. However you can review those jumped levels at any time by tapping on them.