Hi Tom,
I think you already answered the question yourself.
Also be aware that the code of conduct asks all community members to communicate on the community pages (forms, learn, ideas) in English, so that content is readable for all community members all over the world.
Obviously if you feel the need to write in another language consider to send a private message to the other user.
You can always use Google translate to translate a browser page or to translate your text from Japanese to English.
Regards,
Daniel