Rule update?

I was recently informed that typing in Japanese was against the rules on the forums. I won't argue with that, I understand the premise (if there was a Japanese language forum I'd be there), but I did reference the Universal Rules again just now and found no mention of speaking non-forum languages being against the TOS. In the future, might it not be a good idea to add that for those of us that have a habit of falling back on our mother tongue? It'd surely be easier than warning everyone who does it personally! :)

Sorry about that by the way, old habits. (Furthermore, sorry if this post is in the wrong board.)