Honestly, this hadn’t crossed my mind. But now that you mention it… this is a great idea.
As to when and how… we need to find our feet first, and I don’t know the best way to go about it. Maybe a once-over with Google Translate, and then open it up for improvements…?
One concern is customer support/dynamic FAQs, which will be English-only for the time being… a Japanese app with English support could get confusing. Conceptually it’s straightforward, but internationalisation can get messy.
Anyway, thank you for the idea, Rosie! It’s got my vote. When learning German and French, I’d translate everything on my phone to help things along…