Enter-to-submit-comments interferes with Japanese input. It's vital that it be disabled on Japanese.SE. It's been disabled on our main site for a long time; see this bug report:
I thought it was disabled on meta, too, but apparently it isn't right now. Unfortunately, this is interfering with our users' ability to post comments (unless they happen to be less than 15 characters long, since enter can't submit a comment below the minimum length).