[Kitsu]

I have just a quick question.
I often read the difference between the different dialects and accents in Japanese are a lot bigger then in English and such.
Just how big is it?
I'll travel to Osaka and as far I know they speak Kansai-dialect. Will I be able to understand them? In Germany we have also different dialects and such and some people (not me) can't understand them properly. I mean in the end I always have English as a resort, but...