WildStar codes are region-specific. The region you purchase WildStar in determines which servers you have access to (North America or Europe). WildStar does not support cross-region play. To clarify, if you purchase a North American code, you will have access to the North American servers only, regardless of where you are. The same applies to European codes. If you purchase a European code, you will have access to the European servers only, regardless of where you are.
If you are in a different country than another who you wish to play WildStar with, both of you must purchase the same type of code (North American or European) so that you will have access to the same servers.