Yes it does SAPI[1]. There's a few for linux but nothing that's become any kind of standard unfortunately, festival tends to have the best voices but is a bit of a pain to use inside another program in my experience.
It originally used festival but it was a pain to install on the Pi (which I want this to run on) and the voices I tried weren't as easy to understand. I'd love for it to be an option, though.
[1] http://msdn.microsoft.com/en-us/library/ee125663%28v=vs.85%2...