At the moment it is not possible to change the region in which you play World of Tanks with regular accounts. Currently the function of roaming accounts is being tested by our developers and Wargaming employees only. Therefore if you happen to play with a player that has a “RU” or “NA” suffix, it means that it was one of us 🙂
This is also the reason why players like this can’t be found on the EU player list, but only on the list of their respective region.
Whether and when the roaming functionality makes it into full scale functionality for everybody is not known yet. If it should be released, you will find all the details on our portal.