The current practice for translating categories is
The disadvantage of this scheme is, that pages will not show up in the translated category pages until they have been placed there by a translator. It seems like a good idea, that all pages - translated or not - should show up there, but we haven't found a method to do so.
One solution would be for translators to simply translate the category statement on each page - allways the last translation unit. Not an elegant solution, but perhaps workable? Are there any downsides to that?
Just translate the section of the category would create a page/ca untranslated. I think the "solution" report a bug (wishlist) over mediawiki software.
You are right, off course, but it doesn't seem to be very much different from the situation when the translated page doesn't exist at all: In both cases the user will see the original English text. The only difference is that your language will appear in the language selection bar and that the page contains a translated category. How big a difference will this be to ordinary users?
(I am not exactly pleased with this proposal myself - it isn't really a tidy solution, but would anyone notice the difference?)