I have bought from the USPS, is that a foreign country?

and have had no problems as they accepted US currency and my credit card did the conversion and paid them from my Canadian currency.
You do pay a charge to anyone doing this currency conversion service, 2.5% - 5% maybe of the total amount, plus the factor of how your currency compares to the currency you are dealing in at the moment.
The hard part sometimes is knowing the language or having someone there knowing your language. The money part is easy. Easy come, easy go.

But, hey, this is stamp collecting not the stock market.