I could see this causing problems on technical discussion sites as it might consider a block of C code a bad comment. Sometimes there are legitimate reasons to post something non-english, like a blob of numbers or some ascii (or unicode) art.<p>Slashdot has some filters like this on their comment system, but I think they are mostly targeted at blocking ascii art spam.
So you create a barrier by rejecting "bad" comments versus creating a barrier by using signup/captchas etc.<p>I'm not really buying it. The problem in communities isn't really bad writing or quick comments, it's usually trolls who will circumvent something like this quite easily.
Before someone else says it: I know I should migrate to using Git, I just haven't found the motivation yet! I will try to migrate in the next few months though.