Hmm. I guess that would depend on your bank/card provider more than the app. You should call your card provider to find out if they charge a fee for that. I haven't noticed this myself with hsbc.
I think it depends more on who collects than the bank/provider. In my case, the purchase of GDE shows as:
GOOGLE *ROGRO82 GOOGLE.COM/CH GBR
So it's paid to the Google market which in turn pays ROGRO82, the developer of GDE. Since Google is domestic, there's no foreign currency conversion fee.