This will let you talk in any In-game Language:
Code:
/script SendChatMessage("What you want to say","Guild","Orcish");
The First Parenthesis is the actual words you want to say, The Second is which chat you want to speak in. (ie: Guild, Party, Raid, etc.) and the last is which language you want to speak. I havent found a way to speak in /say or /yell yet tho.