The voices/locales that you want to exclude from the random voice selection.
First you'll need to make a profile, you can do this in the top right corner. Type a name in the Name
field (recommended to be descriptive) and click the New
button. Now you can configure this profile by changing the ignored voices/locales. Double-Click on the voice/locale you want to ignore. And now it will ignore that voice/locale, to undo this just Double-Click on the ignored voice/locale and it will be available for random voice selection again. To switch between profiles the only thing you need to do is just switch between the profiles under Profile
and you can even select <none>
to don't ignore any voices/locales.