The principle is: a loan is paid back in same currency and quantity it was given. Without being a condition in the contract (even verbal contract), it is good to give more at time of repayment. This is a kind of beautiful repayment.

If the deterioration of the value of the loan currency is big amicable reconciliation between the parties is recommended and if they do not reach it amicably, an agreed arbitrator or court of law may impose a fair reconciliation after studying all circumstance of the two parties and their economic environment.

Allah Almighty knows best.