I\'ve come upon an idea of using a voice engine on the client-side of the game to make it speak the game chat, but yet I havent seen anything like thise in any online project, since idea seems interesting. Such a function would enable users not only to see, but to hear other players, it wont eat colossal amounts of trafik as real voice translation, and the speach engines i\'ve seen so far a not so bad at speaking.
To the technical side:
The easiest way is just to sent incoming chat messages to the speach engine, even external. I havent yet seen the client source, but i think it can be done easily.
The better way is to compile engine directly intio the game. Of course server should send some aditional bytes when the player speaks - his location and voice prefences - at least his sex - male/female voices differ ) Location is needed to calculate loudness of the voice the player hears and its direction