C++
When you need to get down and dirty for apps on platforms like Android and Windows, then C++ can be the answer to your object-oriented dreams. At this point, C++ has been used to develop apps for virtually every purpose on pretty much every platform that exists. Programming skills are widely available and the language is a well-known quantity. It's not trendy or ultra-modern -- it's been around much longer than smartphones -- but for low-level programming it's still the go-to language on platforms that aren't fruit-themed.