If you use JavaScript, you probably just run it in the browser (unless we're talking about node.js or something). And if you really need it, there are quite a few tools that help you pack that web app into an Android app afaik (Cordova? PhoneGap? Totally blank here, never used these). These tools also give you quite a few programming interfaces so you could integrate it with the OS.
C, C++, C#?
C# is something completely different, I often call it "Java that's not fucked up by design". It's a language, it compiles to byte code and runs on Mono/.NET. It's sort of cross platform, so you can, for example, take FreeSO executable and run it on anything that has Mono/.NET on it, +/- minor adjustments to code. Oh, and it's object-oriented, just like Java.
C++ is basically C + more stuff. The difference is, C++ comes with:
OBJECTS!
CLASSES!
POLYMORPHISM!
INHERITANCE!
METHODS!
and all that stuff that let's you write OOP code (you should totally google this up, if you don't know what I'm talking about). Both C and C++ compile to binaries, you can't just run them on random OSes, but unless you're using non-cross-platform libraries, you could grab the sources and recompile it, so that's something. It's quite fast, since these are just binaries.
Monogame - framework for gamedev, it's compatible to some degree with XNA (which I guess was abandoned like 5 years ago?). It let's you code games in C#, obviously. @
RHY3756547 and @
zc456 can tell you more about it.