Sweden didn't opt-out of the Euro. They agreed to adopt it when they joined. Then they held a second referendum on the Euro and rejected adopting it, that referendum has de-fact no legal meaning. Currently Sweden stays out of the euro by not joining ERM-II as is required for minimal of two years if they want to adopt the euro. Denmark has opt-out clause, they can cancel it with a vote when they want to and adopt the euro quickly after that.
As for Russia. They are preparing for war with Europe. Russia wants what they don't have. What that is EU and what EU has. Prosperity and riches. Putin wants that.
He can't have it and is never going to get it.