In Die2Nite, how do you mix pharmaceutical products

Simply placing decorative objects in your home is enough, there's nothing else you need to do. You'll gain the effect of the item as long as it remains there.

The padlock you found prevents other people from stealing from you when you're out of town. Other items may provide decoration points which are granted to your soul when you die.

Die2Nite may not available from Germany still because there's a German-only version of the game (and a France-only version of the game too, for that matter) that has been around for longer and is more complete.

This'll change as the "worldwide" version of Die2Nite grows to feature-parity, possibly. Motion Twin has hinted, however, that each community may very well go their separate ways for the time being.

That said, proxy and VPN would work. I haven't checked their terms, however, as I can't find them.