During the 2022 Russian invasion of Ukraine, Russia has unilaterally demanded that "unfriendly countries" pay for Russian natural gas in Russian rubles, despite the existing contracts specifying payment in dollars or euros. At the end of April 2022, Russia halted gas deliveries to Poland and Bulgaria, for which they had contracts for and had paid on-time in the currency required by the contract.
Is there any way that Poland and Bulgaria can sue Russia for breach of the contract? If so, in what court can they sue? And what remedies can the court provide, if it rules against Russia?