SUMMARY

After installing the software and letting all configurations to default when clicking the button speak i got the error:

using null output device, none available
qt.speech.tts.flite: "Failed to start audio output (error 1)"

STEPS TO REPRODUCE
1. run: sudo apt update
2. run: sudo apt intall kmouth
3. run: kmouth
4. write a text
5. click in the speak button

OBSERVED RESULT
No sound is emitted and in the terminal i can see the error:

using null output device, none available
qt.speech.tts.flite: "Failed to start audio output (error 1)"

EXPECTED RESULT
That the sound representing the word i tipped is emitted and there is no erro in the console


SOFTWARE/OS VERSIONS
Qt Version: 5.12.8

ADDITIONAL INFORMATION
After the error occurred i tried installed the Qt package with the command:  

sudo apt-get install qt5-default

But nothing changed.