I'll try to answer this - you can't actually talk anything but English here as it's an English speaking server. it's that way so we all can understand each others. However you can add words here and there while keeping message understandable on English. Example can be taken off Kusari or Rheinland where they use various cliches like Konnichi'wa, Guten Abend, Gaijin, etc - you've got it. So you can style your message and yet keep it understandable for the rest. This way various "Previet", "Tovarisch", "Laowai", "Nihao" etc are more or less acceptable to be used for style.
Just don't forget to make sure message is understandable in English.