And do it. There's plenty of FOSS projects who could do with some help. When you've got a job to do, you'll get the idea of what tools to use.
Maybe it's kernel, maybe it's AJAX. Find the job and then find the tools. If you're any good, a new language will give you a week of pure panic followed by....oh, I get this....
My nightmare has been people who had deep, even obsessive, knowledge of X, X++ and Z-- and little ability to analyse the problem in the first place.
Except Cobol, of course. You're safe there.