[orless]

This seems quite unrealistic and inefficient to me. OP would have to find an open source project (with a good community) which would match his/her skills and accept him/her as a contributor - which is a challenge on it's own. Then there will be hardly any feedback on the written communication (correction of mistakes or style etc.). And no spoken language.

I know a lot of people who learned English by singing songs, but hardly anyone who've learned English in an open-source project. And believe me, I know much more codes than singers. :)