I've read on many topics that shopkeepers are supposed to get new and different items everyday, but this simply doesn't happen for me. Is my game bugged?

I have the latest unnoficial patch and the resolution update.

Do this:

Go to a specific shopkeeper you need to restock. Talk to them and open a trade window with them. Close it, then pan the camera as far away from the shop as you can; the shopkeeper (and/or possibly the container in which their stock is kept) needs to be off-screen. Now hit the sleep/wait button and wait a full day. Open a trade window with the shopkeeper again, and their stock should have refreshed.

Normally all that should be needed to make a shop restock is to get the shop off-screen and wait until the following day.

Ah thank you very much!