Using FlaggedRevs to allow reviewing translations
There is nowhere near enough review capacity to for mandatory review. I would be surprised if even 0.1% of all translations were reviewed by the new review feature.
Certainly, we wouldn't want to have review as a requirement. I rather wanted to have it as an option.
I don't know if the current FlaggedRevs have a functionality for this, but I think it would be helpful if people can voluntarily mark certain translations of theirs as 'unsure' when they think so, and another person can find a list of entries with those mark to clear or fix them.
We have !!FUZZY!! and the translation review feature already available, you should try those.
Would it be possible to get a list of messages with !!FUZZY!! at once excluding untranslated messages? And, could you point me to a relevant documentation of the translation review feature?
See also [1] and soon mw:Help:Extension:Translate/Quality assurance. If you're interested, you could ask a Japanese translation reviewer to give you the right, but I don't see any (active) one so perhaps you can ask it here if you want to work on this.