The virtual table read function under Document > Table Read uses the voices installed on your system for its built-in speech functionality. (These are different on Windows, Mac, and Linux — Fade In keeps track of what voices are selected on which operating system.)
The method for installing additional voices depends on what operating system you're using.
You can install additional text-to-speech languages under Windows Settings. Click Start then select Settings, then type "voices" in Settings search. It will show you the settings page for managing installed voices.
You can install additional languages by opening System Preferences from the Apple menu. The actual location of speech settings changes slightly between macOS versions. In macOS 11 (Big Sur) it can be found under Accessibility > Spoken Content. From the "System Voice" dropdown, select Customize to access the list of available/downloadable voices.
Fade In currently uses the espeak-ng speech synthesis package.