Rev.io supports international addresses. To create the countries available for selection, go to Settings > Countries.
Simply click to add or remove available countries. Removing a country from this selectable list will not cause any issues with addresses currently using this country.
On the second tab of the Countries page you control how the countries are displayed in the various drop-downs across your system. Simply drag and drop the countries in this list to re-order.
Once a country is configured you can configure the states and/or provinces available for that country under Settings > States and Provinces.