Susie, this is not about having one currency internationally This is about giving them an equal exchange rate.
In other words, because South African currency has been given a bad grade, all the people in South Africa get paid less for their goods.
The problem was that the Greek government owed other governments and businesses money that it could not repay. This had nothing to do with the worth of the currency. This was the foolhardiness of the European Union of lending Greece money when they didn't have the economy to pay for it. This didn't bring the currency down. It made the people who lent the money unable to get it back. If the banks hadn't been greedy from all the potential profit they were going to make from interest, it wouldn't have happened.
It's the same sort of foolhardiness in China lending Africa masses amount of money. They have now written it off because Africa can't pay it back. This has nothing to do with the exchange rate.
It's about speculation, not about giving a fair exchange rate for coinage.
If I am living in South Africa, and I earn R20K per month (about $1000), I would still pay the same price for an international airfare, and thus be unable to afford it. $20K is a good salary in South Africa.
We're still paying the same price for goods, but our currency is downrated so that banks and exchange companies that speculate on currency pay us substantially less.