If you are a metalhead, you can go anywhere in the world and find good people if you've got a band shirt or recognize one on a local. Language isn't even a problem because there's a kinship you don't really find in other genres. I've been to multiple European fests, not Wacken sized more underground, by myself and always met cool people. Drank with Belgians, Austrians, Polish, German and Aussie metalheads who've all been real friendly and fun to hangout with during the festival. As long as you're not a dick and are there to appreciate the music, everyone is relaxed, drinking and there to enjoy themselves.
I've also been to shows in Bangkok, Tokyo, Osaka, Yokohama, and Seoul. Same deal. If you're genuine and not being an asshole, you'll have fun.
I don't know about it being the cleanest because I've drank a lot at every fest haha. People are there to buy merch, too. Sometimes your only chance to get a lesser known band's shirt is at that show and it is cash straight into the band's pockets.