Maybe a stupid question, but is there a way to install Book 2 without having to download the full 4.4 GB installer? I already have Book 1 installed.

Thanks.

I haven't tried the installation here on GoG (so I don't really know what's in that installer file), but the Steam update was almost as big (3GB), so unfortunately I don't think you can avoid the big download.

Ok, thanks. I guessed as much so left it downloading after I posted. It has now finished. Wish GOG could do updates rather than them just uploading a new installer, but I guess their system makes it unavoidable.

can i just install book 2 over the existing book 1 installation or do i have to uninstall first?

yes, u dont need to uninstall book 1. when done, u can select both books. old savegames are still selectable.
if u want to play the game in german, i would wait a week for the language update. at the moment theres only english audio.