Does the gnome-speech "test-speech" application work for you?
No, it segfaults, see the output below:
Attempting to activate
OAFIID:GNOME_Speech_SynthesisDriver_Festival:proto0.3.
Driver name: Festival GNOME Speech Driver
Driver version: 0.3
Synthesizer name: Festival Speech Synthesis System
Synthesizer Version: 1.4.3
Enter desired gender ('m' or 'f'): m
Enter desired locale, or 'all' to display all voices: all
1. kal_diphone (language english)
Select voice: 1
** (process:7759): WARNING **: Failed to send buffer
Segmentation fault
bram bramd:~$