But now there’s a proper solution! The trouble is caused by the Comment Quicktags plugin that I’ve been using for years. Being an old plugin whose original author has moved on to other things, it didn’t understand the L10n thingy, and so it broke. As is so often the case with WordPress thingies, somebody has stepped in and weaved some magic. In this case, the credit goes to Ibrahim Ali Faour who has released Comment Quicktags Reloaded. If you’re using WordPress 2.2 and you’d like your quicktags to work on your comment form, this is what you need.
Thanks to Weblog Tools Collection for another useful suggestion.
 Not being a coder, that’s the only kind I could come up with