I don't know. It's funny, I know words that you would't expect me to know but I don't know words that I should know!  I get really fustrated when I am in immersion, my mind doesn't process as fast because I am still translating. It isn't that I do not understand, but the words are not second nature.

At the moment you know enough vocabulary to express yourself without returning to think in your native language. When you know the word and sentence in Spanish, you don't think back in English. Automatically. It switches rapidly and goes unconsciously. When I speak with my daughter we can switch 'code' every minute (Dutch/Spanish back and forward). At B1 I would presume you don't think in your own language anymore.

I stopped mentally translating from English to Swedish when I was thirteen and we visited a friend in Egypt (a Swede, a friend of my grandmother) who knew someone at the American embassy there, I believe it was, and (naturally) the guy only spoke in English.This is the first time I realized that I understood what was said when someone actually spoke in English. It was a weird experience, I can recall it still. At that time I had had English for four years in school. Back then you were otherwise exposed to one language only, most of the time (before Internet, and few TV-channels). So the answer to the question is that you stop translating once you've (1) got a sufficiently large vocabulary and (2) are sufficiently immersed in the language.