Even having category redirects work properly (so that if
[[Category:Foo]] redirects to [[Category:Bar]], putting an article in
[[Category:Foo]] means it shows up in [[Category:Bar]] - much like
redirected templates work) would be most helpful in allowing Commons
to use languages other than English for its category tree - so that
different-language names for the same thing would work the same, e.g.
[[Category:Horse]], [[Category:Cheval]] and [[Category:Hauspferd]]
could all point to [[Category:Equus caballus]] and Just Work.
- d.