There has not been a country that officially approved the use of bitcoin, the main factor because they are still using fiat money for all transactions. Bitcoin will never replace a fiat money because bitcoin is decentralized and could not be in control.
i agree with you bitcoin can't replace fiat money
bitcoin until now still not ready regulated, have not physic, if can replace fiat money must have physic
but bitcoin this now is number one digital curency, the best payment curency and easy use
The other reason is due when Bitcoin replace the national currency of a country, Bitcoin could collapse the national currency. Just imagine if the national currency flock switch to using Bitcoin, Strength of own national currency will be loss all of that affected to a country.