The language probably has a lot to do with it as the large percentage of internet porn buyers are English speaking. Plus solo girl sites rely on the surfer almost falling in love with the girl and its difficult to do that if they are speaking in pidgeon English - no matter how good looking they are.
One possible site you may want to check out though is:-
http://www.haileyhardcore.com
This features Czech model Simone Styles - a very attractive brunette who speaks reasonably good English as well.