Ii think we made a mistake when we called this a “four day work week” instead of a “32 hour work week.” Too many people think it refers to four ten hour days, which many people already do.
This is similar to when we transitioned from the 60 hour, six day workweek to the five day, 40 hour one we have now. Hours get reduced, pay stays the same (no change for salaried, 20% increase for hourly).
I’m not sure that’s exactly what the Germans are looking at, but that’s what the US proponents are fighting for.