It sports a text to speech API, among others, and a command interface for extensions. The system supports English (both Brithsh and American) as well as Welsh and Spanish. You can also find packages for Finnish, Polish and Russian to name a few. And if that wasn't enough the whole lot of it is published under the BSD license - meaning it's free and open source.
To get started we'll need a few packages: Obviously first we'll need festival and xsel.
cat << eof > talk.sh
xsel | festival --tts --pipe
cmod +x ~/tts.sh
Next bind mod4+z to ~/talk.sh. From Ubuntu key bindings are found under System, Preferences, Keyboard Shortcuts
If you run into the error Linux: can't open /dev/dsp
(Parameter.set 'Audio_Command "aplay -q -c 1 -t raw -f s16 -r $SR $FILE")
(Parameter.set 'Audio_Method 'Audio_Command)
" >> ~/.festivalrc
The speech rate can be configured in /usr/share/festival/voices/english/kal_diphone/festvox/kal_diphone.scm
under the setting "Parameter.set 'Duration_Stretch" -- the lower the value the faster the speech rate.