Kotlin might be an option, it's new and somewhat an improved java. Android adopted it. But my first answer always is: Python! Good to learn, easy to integrate, platform independent but hardly used for mobile apps (please prove me wrong as i would love to see it successfully used). Python allows for a whole slew of different programming paradigms.
Once you know programming, learning yet-another-programming-language mostly isn't that difficult (except for lisp and a few others). It's getting to know the useful libraries and tools that takes up the bulk of time.