I don't know what basis you base your claim that China and Russia are using cryptocurrencies for their transactions, but according to my understanding, they don't need cryptocurrencies like bitcoin, XRM... let alone centralized stablecoins.
After the Moscow Currency Exchange was banned from using the dollar and euro for international trades, Russia really had big difficulties with payments under interstate agreements. Long before that, Russia tried to switch to using the Chinese yuan, but there were big difficulties with the yuan as well.
Therefore, Russia really wants to try to use cryptocurrency for these purposes. This is evidenced by the bill No. 341257-8 submitted to the State Duma, which allows the Central Bank to launch an experiment on September 1 to create a platform for using cryptocurrencies in international settlements. But Russia's main trading partners - China and India - generally have a negative attitude towards cryptocurrency and it is difficult to imagine how they will trade with it. Moreover, as we know, cryptocurrency has very high price volatility, which introduces a certain instability in settlements.