Europa is a specific styling that is applied to portable infoboxes. The ability to use gallery tags is a function of portable infoboxes itself. Therefore, using gallery tags should work whether or not it is specifically a Europa infobox. It should work on UCP.
It didn't work because you have extra stuff in it. This is what you have right now.
I made the change on the page for you. You can use the page history to see what I did. What I said was the issue was only part of it. Apparently, when using gallery tags with a portable infobox, you need to use lowercase letters for the tag's name. <gallery></gallery> works but <GALLERY></GALLERY> doesn't.