The "Text to Speech feature" is working now on Proton Experimental on the condition that you installed the "Proton Voice Files", and there are a couple of quirks.
After installing "Proton Voice Files", and forcing Proton Experimental:
Start the game and observe that the tech to speech is now working
The "Text to Speech" in the options menu still shows "error" for voice. And you have to enable/disable the "enable dialogue" option everytime you launch the game, it is otherwise disabled by default during gameplay.
Log of playing the game with TTS enabled:
steam-2717480.zip
Compatibility Report
System Information
I confirm:
Symptoms
Game is unplayable/does not load in properly when starting new game with default Proton. With experimental-bleeding-edge-9.0 game loads in without issues and is fully playable, but the issue is that Text To Speech (TTS) feature is not working.
Note! This issue can not be replicated with the demo of the game. The demo works on default Proton, but it lacks the TTS feature and looks and is functionally somewhat different.
Reproduction
Proton Log:
steam-2717480.experimental-bleeding-edge-9.0.log
In the logs I see "\system32\Speech\Common\sapi.dll" so I guess the game is using Microsofts Speech API.