There are a lot of popular languages, but in my opinion the one you should learn is the language that best solves the kind of problems you are interested in solving. Once you know how to program, you'll be surprised how easy it is to learn multiple languages. Programming languages are a lot like tools in a toolbox. Some of them are general-use, while others are really good at solving very specific problems.
If you want to make things for an Android phone, you'll have to learn Java. It's more complicated and has a slightly higher learning curve, but it is more powerful too.
If you want to build something for an iPhone, you'll want to look at Swift.
There are so many possibilities and things to explore.