I'd recommend picking your second language after you finish CS50. This year the latter portion of that course is taught using Python. By the time you finish the course you should have at least an introduction to C and Python and will be better prepared to make a determination regarding which next language makes the most sense for you.
If you want to go into Android development, Java is a must.
Languages I see strong need for over the next 5 years: Java, C++, Golang, Python, Rust, Clojure.
There's a bunch more languages that'd be great to know as well, it all depends on what you want to do.
I'd stay away from PHP and Ruby personally. They were the "junior dev" languages of the past decade and there is a metric crapton of really awful PHP and Ruby code out there. If you don't focus on them, you won't be stuck trying to debug the gastly mess that the last decade of "I'm going to learn the minimum and then spew crappy code for anyone who'll hire me" junior devs created. The Ruby code isn't as bad as the PHP but neither language attracted (overall, I know there are exceptions) the caliber of talent that Python, Java, or C++ did.