Hard to say on USD. Neither of them has a particularly good currency. China's is leverage and their banking so opaque you can't make valid statements about it. Russia's is so tied to oil markets that trading oil in it makes little sense.
This is how an exchange currency works. If I'm a melon farmer in Uruguay and I want a Belgian tractor I can't pay for it in Uruguayan pesos because the Belgian tractor factory can't spend them and the Euro isn't much good here either. Say I'm selling melons to Turkmenistan. Well we can't really use each other's currency either.
