Pico text to speech engine for Linux was developed by SVOX. It can be found in the android open source repositories and is covered by an Apache 2.0 license.

https://packages.debian.org/bullseye/libttspico-utils

To install, open linux terminal and type: sudo apt-get install libttspico-utils

To test, type this command in linux terminal: pico2wave -w lookdave.wav "Look Dave, I can see you're really upset about this." && aplay lookdave.wav