Hi!
Where are the names of those units translated at the moment?
I assume on the wikidata items for them, those are just labels for wikidata items (as units are items).
If these are MediaWiki messages, grammar rules for them can be added fairly easily. If I can see where they are now, I could probably make a quite demo patch to show how it can be done.
I don't think we can put grammar rules in labels, that's why I proposed a special property as an option.