When I was a teenager, I found very significant changes in fluency when I was studying and learning to think in foreign languages. In my case, I noted my thought voice and oral voice in German was crystal clear - a huge change from my faltering American voice. As an adult, the differences are less noticeable. I just spent a year in Japan... and my Japanese speech fluency was much more problematic than my English fluency. The benefit seems to come if I just get wistful and lay back (as if into a sofa) into the endeavor of focusing earnestly on learning to think in the language. I think there's something here that has to do with my tolerance for daydreaming, oddly enough. I wonder if all of us have this "Language Acquisition Device" that Noam Chomsky talks about, and whether it can kick in if we open ourselves up to it. This might not be always be a safe thing for an older person to do.... but maybe there's a happy medium to be found, somewhere.