Tested in French, and it's Google voice, it's very good. On my Android device, though, I've installed better voices, paying, it would be cool to be able to use Android voices with this extension, but I don't know if it would be possible one day. EDIT: I let a very good review 2 years ago, I don't know if the addon has gone less good, or if it's because I use it on a different machine, but the voice, in English or French are so so so robotic, that I can barely understand what it says.