Downloading additional voices from command-line
You can predownload the voice files to your App/Python package (or however you are distributing your app), and then write a script to move or copy the voice files to this folder:

/System/Library/Speech/Voices/


So:


  
  Download the voice files on your development machine
  Wrap them inside an assets folder or something like this
  Part of your Travis script can be to move the files first in the Voices folder on the mac
  And after that, you run your tests/other scripts