[KyleGoetz]

I stopped having to translate in my head after a year or so of doing Japanese conversation over an hour a day, three times a week, with a university club. This was, of course, in addition to the five or six hours I spent in Japanese language classes at university and the hour or so of homework I worked on every night.

So probably twelve or more hours per week of practice for a year got me there, where about 1/3 of the time was with native speakers in native situations. 1/2 was in a classroom with a native-speaking professor only teaching using Japanese (no English).

Of course, this was only for a limited number of settings and conversations. Many topics were (and still are) outside my linguistic grasp. But that has little to do with thinking and more to do with plain ol' vocabulary size.