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.
bitcoin for today is unstable, especially in terms of price. bitcoin is very difficult to replace fiat, because it is basically a country does require a fiat to tax thing or something. Fiat also give the state extra money, such as tax payments and others. if using bitcoin, I think, the state will not have the extra money from the public, because with bitcoin, we do not need to pay taxes.