If W2 doesn't start on current Ubuntu 64 bit releases because of a missing libgtk-x11-2.0.so.0, you'll need to install the package libgtk2.0-0:i386 in addition to the packages listed under "System Requirements" in the GOG store.

You can do that easily with this terminal command:

sudo apt install libgtk2.0-0:i386

I've asked the GOG support to include it on the store page.

edit: GOG added libgtk-x11-2.0.so.0 and libsdl2-image-2.0-0 under System Requirements on the store page. My thanks to their support staff.