I would like to tell you something I discovered when I started using Waze. I think it maybe applies to all countries except US. That's why I post it in this forum.
In the beginning, voice commands didn't work, Waze only recognized "Casa" or "Trabajo" (for Home or Work).
After a lot of trying I discovered the reason. Outside US, Google Now suggests you to have multilanguage option selected, to be able to activate 'Ok, Google' in all the screens. So did I by selecting US English as main language and Spanish language as second language. In some way, selecting several languages there makes Waze voice commands not working.
The way to solve it is selecting only one language for Google Now, and it has to match the language it is selected in Waze (I have checked this also). I have Spanish, and only Spanish, as my language in Google Now, and the same in Waze. This way, voice commands work perfectly in my Android phone.