how long to learn one programming language ?

None of the Programming Languages are small enough to learn everything in them, it could take years and you still wont learn everything in one language.
It's about Learning Programming Technique and understanding Flow of Execution while making an algorithm.
Doing Yourself can take lot time if you don't have experience.
Taking Training from some decent institute might help. They usually provide 3 to 6 months course for different languages depending on your selection.