That's not really how that works. IMF can demand their loan be repaid in whatever currency they want. Its totally normal for international loans to be denominated in a currency other than the recipient's legal tender, particularly for high risk countries (although that is usually bad for the recipient)
They don't want Bitcoin in exchange. Seems entirely reasonable to me given how much the value of cryptocurrency fluctuates with low predictability. They could get paid in it one day and lose half the value the next.
This is why otc tradfi crypto futures are needed. You can buy a train car full of corn a year out trivially on a liquid futures market, regardless if corn prices fluctuate wildly you will pay what was agreed. Listing BTC derivatives would solve the predictability for fixed loan terms.
