I have no idea what that’s about. The data item scheme has evolved over the years; it might’ve been an early property or something that has since been removed. Or maybe a reference to the practice that you originally asked about, not sure.
In any case, I see no point in translating raw English tag IDs to raw French tag IDs and so on, since it could mislead mappers to actually use those translations as raw OSM tags. Anyone who wants to improve discoverability and usability in other languages should focus on translating descriptions and optionally providing translated aliases.
Wikibase recently introduced a universal fallback locale mul, sort of like how name=* behaves in OSM. Once we upgrade to that version of Wikibase, we may have the opportunity to migrate the tag ID from en to mul, to reduce the awkwardness of only specifying a label in English. But that may still necessitate changes to how iD and other software packages are consuming data items.