>>135 Raided with one for a year, actually (though, to be fair, his enunciation was not). Reminds me, maybe the least understandable guy I've gamed with was 10 years ago, a poor bastard in a different guild whose native language was Gaelic. He wasn't properly educated in English for some reason; meant he basically had nobody to talk to online and everything he said made you think you had a stroke.
Here in the Old Dominion we've got a couple of (rare) accents that exhibit some similar vowels to some northern "tongues" despite them being completely unrelated. And the preeminence of regional slang tends to be played up a bit, unless you work in an old industry. What I'd consider a dialect by other language's standards is Scots.
Though, I don't consider myself good at hearing through accents, mind you; I consider myself poor at hearing spoken communication in general so it equalizes somewhat.