English is my first language and even in English spoken games I often put on the subtitles because it is often hard to hear what is actually being said especially in scenes where there is a lot going on, i.e. lots of sound effects, so subtitles in and of themselves do not bother me. With that said I would think and English spoken (no accents) game makes sense.
It would be nice to pay homage to the local dialect in some ways. Others have mentioned latin in churches which I think would be great. Maybe also some of the banter that goes on amongst the townsfolk could be in Czech. Could be a way for none Czech speakers to learn a few phrases which I would find fun/interesting.