@raven-worx I don't have any experience with TTS either, also I can't find much info about the current infrastructure on Linux, resp. on KDE. I have installed speech-dispatcher. And I can make it speak in the terminal, using its own spd-say command. I'm not sure how speech-dispatcher and flite are related. I think speech-dispacher is an abstraction layer / daemon, and flite is one of several "engines" it can use.

spd-say --list-output-modules says:

OUTPUT MODULES
flite
cicero
generic
dummy
espeak

The following packages that seem to be relevant have been installed:

speech-dispatcher libspeechd2 flite libflite1 speech-dispatcher-flite libqt5texttospeech5 libqt5texttospeech5-dev qtspeech5-flite-plugin

Note that no qtspeech5-speechdispatcher-plugin (or similar) exists in the repo. But looking at the Qt Speech sources, it seems there should be such a plugin.

Anyways, when I build an application for testing ....

QTextToSpeech::availableEngines() returns "flite" availableLocales() gives "en_US" and availableVoices() says "kal16".