If there is one language that you should learn for app development, it should be Python because it’s easy-to-learn and it’s great at readability.
Python is a powerful high-level language that can be used to create android and desktop apps from scratch. Just to give you a hint of how powerful this language is, Dropbox is created in Python.
If this isn’t encouraging enough, here is a list of some other apps and websites developed in Python.

Calibre
OpenStack
BitTorrent
Quora
Reddit
Spotify
Instagram
YouTube
The list can go on and on…

Well, the potential is there. You can create any type of mobile app with Python. Learning it is not a big deal since it is one of the easiest languages around.