Hallo!
Bryan Jurish is the speech expert in pd world ;) ... you can find all his stuff here: http://www.ling.uni-potsdam.de/~moocow/projects/pd/
There are the ratts and flite externals. I think he also made an external for the mbrola speech synthesizer, but did not release it ...
Yes, for the pd radio I used the flite external, which is quite okay but only english ... If you want to make other languages you can use mbrola via a shell script (I can send you one if you are interested).
LG Georg