I understood that you entered category on “Admin Post”, which I assumed to be page like this: /wp-admin/post.php?post=xxx&action=edit
There is no way to enter translations there. That is why I asked, where did you enter translations. Which page did you use to enter translations? I would assume it was page like /wp-admin/term.php?taxonomy=category&tag_ID=XX&post_type=post, is that right? Maybe screenshots would help.
In any case, if translations are entered and all looks good at admin side, then your theme may need integration, althogh I would dthink it is unusual to need integration on category names, but who knows how they wrote your theme. Which theme do you use, BTW?