The add-on installs available voices for the settings ring.
In the settings, select the desired languages for which you want to select voices.
If the voice language has not been defined, such voices are grouped in the "unknown" category.
Then, in the second list, mark the voices you want to add to the NVDA settings ring.
Save the settings and restart NVDA, after which only the selected voices will be displayed in the settings ring from the entire variety of installed voices.