I played it a year ago for the first time, in english, also because I felt confident I would understand everything and wanted a bit of english practice.
Oh boy. It is really hardcore. I could not play on weekdays, it was too much work. On weekends though, I could play for 6 hours straight - what an english boost!
Though there is a lot of unusual english - "pike off, berk" and the like.
anyway, I recommend playing it in english. But my second playthrough in a few months will be with czech translation (which is supposed to be great) - I do not want to work on it again and want to have it more comfortable : )