If you manage to get this done for OpenCart, you might also consider some others.. like osCommerce, Prestashop, Magento...
see:
http://en.wikipedia.org/wiki/Comparison_of_shopping_cart_software
Magento claims to have 90.000 shops using it, PrestaShop over 10.000, osCommerce 12.000...
Getting just one of these systems would open a lot of doors... and they already have multi-currency options, so it should not be too hard..