Wow, after playing some more I have to say this translation looks amazing. It really looks like FF7 was meant to be played in German from the very start.
I had never realized before, but there is a strong connexion between FF7 and Germany. Not only towns have German names (Kalm, Nibelheim, Mideel) but the houses are also clearly of traditional german architecture. Midgar is split in two halves, where enormous equalities between quality of live between both halves, just like Berlin was, and is also incredibly endless huge, just like Berlin is. As for ShinRa, it obviously reminds the strong military and totalitarianism past of Germany.
It would be awesome if I could get a dicionary embedded in the playstation to look up for unknown words (there is many many many of them everywhere...)
As for dialects, it seems Jesse speaks swiss-german. For the others I can of course not recognize them but that's still probably a good idea.