Do you program for both Java/Android and Ruby currently? I'm developing for Android but also I'm generally like Ruby and I have an opportunity to get into free

Do you program for both Java/Android and Ruby currently? I'm developing for Android but also I'm generally like Ruby and I have an opportunity to get into free Rails courses. Does it make much sense to know both things from the career benefits point of view? Rails as a backend for Android app maybe? Or should I just continue improving my Android skills