Hey, that was me! I have the RH10 with a completely dead screen. I purchased the MC40ELK because I saw someone said it helped them navigate it much easier than the supplied remote. But I didn't think it would be in Japanese (duh!). This MC40ELK is not from Japan (UK).
An old thread had some guidance with the Japanese options you should select, but it's different Japanese from that of my remote (kanji vs katakana). Here's a pic: https://imgur.com/a/Lm8iVV3. Using Google Translate it does indeed seem there's no Language option. That's why I was hoping for a hack or service mode or something.
Thank you for posting this on my behalf, sfbp. Hopefully we can get to the bottom of this. It seems mad that the remote gives you a different menu to the RH10 itself.