I know it would seem snobbish to block the posts from someone typing in very poor english, but if it's disruptive to the forum as a whole I would likely do it. It can become a bigger distraction to conversations if users are constantly having to explain that they don't understand what the poster is trying to ask or trying to state. It will just break up conversations about other things into discussions about their lack of understanding of the English language. I can't speak french, for example, so I wouldn't try to join in on a discussion in french and expect everyone else to try and decipher what I am saying tediously.