Not even sure this counts as a bug, but the title pretty much says it all but I’ve included a screenshot. It said the same thing for the 4 or 5 months I flipped through when I noticed it.
That’s an interesting aspect of the problem. Perhaps that is related to something I noticed in my review of the leaderboard view code:
Each leaderboard column is rendered via the leaderboard_column partial. I noticed that while the plural for observation and species are each correct, it passes noun_plural: 'identification' as the plural of identification! I think that at least accounts for the missing translations, and possibly also the bug itself. I don’t have a way to test it myself, though.
Compare with the similar code for leaderboard on the users page (i.e. https://www.inaturalist.org/people ) that does correctly pass noun_plural: 'identifications' and doesn’t suffer from this bug: