I hope you can make sense of an English reply. My Spanish is terrible.

It’s not possible to override the duplicate slug restriction within the same object type. This is because child categories need to be able to be queried without their parent. SQL would not know which child to return if there were duplicate child slugs.

You can have duplicate slugs amongst different object types, for example category and tag objects can both have the same slug because the taxonomy is always part of the query, so there is never any ambiguity for SQL.