There are enough players who don't speak one bit english, or not very well, and those still play. They often stay amongst themselves and RP in their native language, but I've also heard of people, who improved their english skills in those native-language guilds, since they had a 1:1 translation of vocabularies and whole sentences, provided by guildies, who's english was better.
Joining a non-english-speaking guild is not neccesarily the worst you can do.