Under such a set-up, it may be easier if lending was simply abolished. Rent until you can buy, etc..
If Governments wanted extra currency and did not have the holdings to give to the repository and could not buy more from other parties or extract gold and or silver they simply could devalue the currency based on existing holdings at the international repository where the international mint issues out more currency to the country. This is where it could get interesting if countries want to go banana and not do the work. The countries could raise prices domestically to hit travellers and immigrants despite currency devaluations but that would hurt domestic citizens to. Once governments have new currency they could issue it as they saw fit. Naturally if citizens worry about devaluations they buy their own gold and silver as an option where they can to.
The other thing is with such a setup the international machines at sales point could provide independent data for travellers and immigrants on the cost of living based on price fluctuations within domestic countries along with devaluations so travellers and immigrants and emigrants are fully inform so resource allocation is enhanced through a superior working market for choice
