I’ve noticed as well when adding additional lexicons in my display settings that common names in other languages have a bunch of issues and look like they some curatorial work (names seemingly directly translated from English or scientific names, or the name for the genus or family applied to every species in it, etc.). I’m guessing it’s worse with species in my area since there aren’t many naturalists who speak those languages who interact with those species. I’m not fluent enough in any other languages to feel comfortable searching for proper names or discussing issues with them with native speakers though.
A working group supported by the Canadian government is working on creating French and English names for every species that occurs in Canada, but its methods are questionable and the results are controversial. Beyond that I’m guessing there aren’t many sources for French names of Pacific Northwest species… When searching the forum I was surprised to see that even recently there were issues with French bird names even for species that occur in Quebec.
I suppose this situation is not dissimilar to situations where amateur naturalists are just starting to get interested enough in a particular taxa for English common names to be useful. In those cases common names don’t exist yet and someone needs to invent them. One way of doing this could be that one person creates a guide for the taxa and invents common names, and then other people can decide whether they like those names and want to start using them (or adding them to iNat).