Currently, on wikis that use Extension:Translate for categories, the Special:WantedCategories page gets quickly‑ish flooded with untranslated versions of categories that are marked for translation.
It’s not easy to manually clean that page up, (case in point: Special:Contributions/ExE Boss?offset=20210624102801).
It also makes it hard to find actual wanted categories that aren’t just language variants of the base English category.
I think the request is valid and makes sense, but perhaps the Translate extension is not the best place to implement it. We currently leave category handling to translation admins, so it wouldn't make sense for us to manage categories automatically without better category support overall. There could also be complications, like if one uses translatable categories... then we couldn't just create missing pages automatically without special handling.
I think it would be pretty easy to write a pywikibot or maintenance script to do it periodically where wanted.
Could you explain what you mean here better? I can't think of any reason why if a category is marked for translation and a page gets added to a translation of that category which currently doesn't exist it wouldn't be possible for FuzzyBot to automatically create the category as 0% translated. Sure, this wouldn't address every possible situation, but I can't imagine it causing any harm.
I may, time and motivation permitting, write a patch to do that.