Content Translation server returns array of objects representing adapted categories. Each object has source title, true/false adapted value and target title, if there is any.
Hidden categories are returned and some categories are returned multiple times. There is no info if given category is hidden, that can only be known after additional API call. Here you can see "Category:Pages containing links to subscription-only content" displayed three times. That category is hidden, but returned to client and has multiple instances.
CX1 adapts categories on client side, where ?action=query&prop=categories&clshow=!hidden is used to fetch categories. For "Painted turtle" page, from en to hr, four more categories are displayed: