Why is the breadcrumb of my help center not showing the category in some locales?
Check to see if there is only one category available for the same locale. For categories to exist, you must have published translations for the locale in question. If there is only one category available for a locale, the breadcrumb will not display. This is to facilitate help centers that don't use the category layer, but only include sections nested inside the same category.
For more information, see this article: Organizing knowledge base content in categories and sections