Anyone can explain me how to mark this on my Steam wishlist?

I don't think you can mark collections.

You can use istheranydeal.com by adding it to your waitlist.Just enter "Star Wars Collection - 2013" into the search.

Thanks, I took the code ! I already have it on Steam but my brother sometimes uses my Origin account... He'll be happy for this !

My method doesn't work with this pack in particular, but it worked for me with the Tomb Raider pack, and might help you in the future. I basically put TR Anniversary on my wishlist, because it didn't have a store page per se, meaning that in my region I can't buy it as a standalone game. In that case, you could see Anniversary on my list, but for a ridicoulously high price of whatever the whole pack was sold for originally. Can do the same with Serious Sam, could also do it with the old GTA pack that had the first two games, and I'm pretty sure you can do it with a lot of others too out there, but unfortunately not with this pack.

Most you can do is put a single game on the list and see its price get discounted or something, or use some "third party wishlist generators", if that makes any sense; others already recommended some above.