On Japanese Stack Overflow, the description for the 'No longer needed' flag is still in English:
I've checked other sites (ru.SO, pt.SO) but there it's already in the right language.
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Text for localized sites comes from translations database provided by transifex.com. Each unique string that able to localize (translate) from the original English text has a record in transifex DB. If any string is not yet translated localization engine uses original string. Translations is managed by Stack Exchange users who have access to corresponding transifex project (one for each language). If localized site doesn't have translation for some item there are two situations at least:
Original string not used in localization engine, i.e. no string in transifex. So translators unable to make translation. Hence it's a SE team bug and should be posted here on MSE. E.g. Translation for migrated posts in revisions
String exits in transifex, but not yet translated. Hence it's translation team overlook and should be posted as a bug report on the corresponding localized meta site. In particular discussed sentence has been translated for ruSO after posting bug report Переведите новый интерфейс тревог для комментариев
In this way to know the type of localization bug you need to have rights to access transifex project for specific language. Because current sentence is translated on a couple of sites and as far as I know original strings appear simultaneously for different sites there's bug type #2 and should be posted on jpSO.meta.