Did you even read what you linked here?
You can play any game from everywhere on every PS4, that is true because the PS4 is region free (every support will confirm you that). But of course you can not buy a game in one country and a DLC for it in another......that is what your link is about and this is just logical.
You just have to register a PSN account with the right country (same country as your game) and even this "problem" will disappear, since the PS3 it is this way.