Ok so yesterday everything was fine but now I just tried playing after coming home from work and all the dialogue sounds are gone from the game!! just like that.

I can still hear ambiant sound just no voice, tried using english, germen french voice, nothing change.

Before you asked, no I don't use a headset . I didn't change any hardware on my Pc overnight . No driver or windows update either. It's the exact same computer as last night
So a big WHAT THE HELL? on that one. the only thing that work is changing my speaker set up to stereo instead of 5.1, I get the voices again but it's deffinitly not the same gameplay experience.

Maybe some Mahakam gnomes came into my room to tinker with my PC while I was sleeping?

What mission were you playing?

it seems some people experience the same problem with 5.1 audio systems...
There is no miracle solution, except waiting for the next patch and hoping it will fix this issue.

close down the witcher
try going into control panel for windows
find your sound settings audio out.
If you have multiple outputs enabled, shut off any that aren't your primary.
Now disable the primary output and wait a minute, then re-enable
test to make sure you get sound, then relaunch w2 and see if that fixes the issue

This is the only work around I have found when my audio stops working.