Would it not make more sense to handle this via the central bank? To just take control over the national financial and monetary system? Or do other currencies

Would it not make more sense to handle this via the central bank? To just take control over the national financial and monetary system? Or do other currencies become even more valuable if this type of collusion takes place? I guess the relatively free trade and money flows make full control impossible. Edit: I suppose if you want to import (luxury) goods you need foreign currency...