the tethering of fiat to crypto currency makes it by default an exchange rate prone crypto currency. If the crypto zloty is tradable and gains value on a crypto exchange, people would simply buy zloty at a fiat exchange (cheaper) and buy crypto counterpart for it. This would also drive the fiat zloty price up, making the national economy lower prices (and salaries) in return. If the crypto coin then crashes, the buying power of Poland would be null and it will quite possibly go bankrupt. Either all countries adhere to a decentralised banking system, or one of the coins cannot exist.