Thread:Fingyer/@comment-4791521-20120429134718/@comment-4028522-20120430104125

That seems pretty conclusive to me that you can play with other regions!

I think this is because Dark Souls uses more of a "peer lobby" system rather than the Demon's Souls system of a big main server that handled everything. Personally, I think the Demon's Souls system was a lot better, however with my Chinese copy, I could only ever play with other people that had the Chinese copy.