very interesting topic! I love English, especially American one as my last three lectors were all Americans.
I actually also took BEC Higher (just practicse test) with a very good scoring, although it was pretty damn difficult.
no...it was terrible!!
I'm also eager for slang expressions, that's why I started using a notebook where i do write some new expressions, interesting words, collocations. That's pretty helpful when you watch TV series or movie in original version with subtitles, etc.
(for instance, to make allowance for, douche (en francais son sens est tres different) or pubes)
For the record, Czech language is much more demanding than English, including 7 grammatical cases and an incredible amount of *weird rules*. To be honest, without word correction, I would be very often caught up when writing official letter in Czech