>>>a good knowledge of the language is just a useful tool to communicate, but it is not enough.

I face this problem daily. I work as an interpreter and consistently see people who know both languages severely stumble their way through attempts at interpreting. In my arena, language proficiency does not immediately lend itself to interpreting. But so many people think that because one knows both languages, one naturally can interpret.

Ever try the Babelfish AltaVista translation service (http://babelfish.altavista.com/translate.dyn)? Imagine that kind of translation going on in a doctor's office when it is your kidney in question.