I’m surprised there’d be a benefit to doing this in the JS vs having your database just return all the cases with the name and then you select which one you need at display time — basically in the same layer that’s populating your localized language templates.

That said I’m curious how this manifests with cross-language situations. I guess the Icelandic UI displaying French names would just always use the nomitive case, and likewise for the English UI displaying Icelandic names? I assume this all mostly matters where the user is directly being addressed, or perhaps in an admin panel (“user x responded to user y”).