IDK how you can add more than 17 voices, but you maybe have to add an xml file in 1.3>Defs>SoundDefs. You can create a folder in the sounds>unitresponse and add a new folder for your new voice e.g Male18. Follow the naming of other folders for the files and I guess that is how you add a voice

All speculation through reverse engineering though

it only works if you set the code up for it

oh fair idk

where is the ♥♥♥♥♥♥♥ combine voice

found out how to add more voices yet?

Needs clearer documentation so we can add our own voices. would be way awesome :)

there are mods that add more voices, don't know how to do it myself but they're neat.
unfortunately can't use more than one and manually assign voices from both.
voices from both still work, but only voices from the voice mod with highest priority appear in the mod menu.