Successful currencies meet three criteria:
(1) they are in widespread use as medium of exchange
(2) they serve as unit of account
(3) they are a stable store of value.
Most sovereign currencies fully meet all three criteria.
What about Bitcoin?
So well to the point that there are now a physical store accepting cryptocurrency not just bitcoin as a means of payment. It is not prohibited by the government but they are giving cautions on using bitcoin and other cryptocurrency because of the volatility it contains which is very high. Crpytocurrency in my country are being recognize and doing well in the market.