About europe and america cd keys
Even if your codes are bound to different regions (and you should get the recommended version), you can choose any server to play. So there will be no problem.
Argentina is not in the USA – you should not buy an American CD Key.
European countrys should buy Euro CD keys.
What Michael said. There is no regional restriction on server selection. You should buy a European version, and your friend should buy an Other version (they call the region for Argentina “Other”).