A brazilian business has created an app that allows you to add your own voice to Waze, they also give you the option to download voices created by other users:
http://www.minhavoznowaze.com/

No idea if waze allows the creations of addons to the app, but it is surprising that none (to my knowledge) have shown up before.

EDIT: Link to play store Here
Because of access restrictions on Apple it wont work on iOS.