easy to install?

how easy is vb advanced gallery to be installed?
are there template or php files to edit?

Currently there are 5 PHP files to edit (1 change each), but that will be down to 3 for the next version. Then there is an installer which will do all of the database modifications and such for you.

no template modification?
what about the language? my forum is in italian

No, no template modifications. All templates for the gallery are separate (though still in your style manager) and added with the install file. The phrases are separate as well. While there are a couple that will use default vB phrases, most are unique to the gallery.

and how many phrases do I have to translate?

I don't remember the exact number, but there are a couple of hundred.

mmm pretty many