It's not even remotely true that all of his movies are with accents. Look at Seven, Fight Club, Ocean's Eleven, Fury, etc. That's basically how he talks. Sure he's played Irish and German people and put on heavy Southern accents (like in Inglorius Bastards), but plenty of Americans also do that for a role. One bad interview doesn't mean much either. Just browsing through his interviews gives the vibe that he doesn't stutter.