[htk]

I don't know about other people, but the only way I really learn a new language is by dedicating myself to build a project using it, no matter the size, but it has to be something that you have a clear vision of what you want to build (so you struggle at the hard parts, instead of just changing the course of the project). This will make you search for ways to "say" what you need in that language. It's analogous to going to another country to learn a foreign language.