Answering your question. I think project owner should set the reward in his local currency then you need an axchange rate to convert to different currencies.
If I had to describe the functionality I'd start defining it like this:
- As Platform owner in order to expand to different countries I need the platform to accept diferent currencies.
- As a project owner I want to receive payments from my country or abroad in my local currency.
- As a backer I want to see all the projects in "my" local currency (no necesseraly the same as the project).
- As a backer I want to donate in my currency (or in USD for international transactions)
Mariano