I haven't used Waze in a long time but i seem to recall them having a similar feature a few years back... But they were temporary (promotional?) and may or may not work anymore. Maybe it takes some fiddling.

A reddit thread with some waze voice packs: https://www.reddit.com/r/waze/comments/3pi5yl/waze_voice_pac...

I'd guess it's at least partly because pre-recorded ones can't pronounce street names.

No, really? Got a link?