In order to pay in Rubles, you have to get Rubles first. So you buy Rubles with Euros or Dollars or whatever, thereby backing the value of the Ruble.
If they get payed in dollars they can leave those dollars in the foreign bank and buy rubles with the dollars. But I don’t think that is a good thing right now. They really need dollars, Yen or Euros. The US will keep attacking the ruble. But they can’t attack the dollar. The dollar is getting stronger. The US is causing that. If Russian dollar stores grow, the US will have a tough time attacking. Russia needs currency diversification primarily.
“So you buy Rubles with Euros or Dollars or whatever, thereby backing the value of the Ruble.”
But the ruble was already backed by the oil which you needed the rubles to purchase, thus you’re just playing a shell game.