how long to learn one programming language ?

It doesn't really matter what programming language you start with, as long as you find programming interesting. Of course, I would recommend not to learn very complicated languages until you learn the basics of programming, as they are mostly the same for most programming languages. I would recommend C++ to learn about programming logic, C# is a good option too. If you are more into web development, just go for the classic combo HTML+CSS and then Javascript to actually start programming.