What is the origin of the Latin suffix -alis/-alia? Can it be an Etruscan borrowing? Is Russian adjectival suffix -аль- a borrowing from Latin?
This is actually an very intriguing subject. I contend that, in fact, -alis/-alia are related to -ly/-lik/-lich, and that Hittite actually exhibits this feature in the autonym Nešili ([language of] Neša+ili). If you would like to ascertain whether Russian (about which I will confidently say I know very little) borrowed -аль from Latin, first look at the relationship the two languages have had over time. Then look at the words on which the morpheme is affixed. If they appear to be mostly borrowings, you could probable stop there. However, if you find them veritably Slavic, look to other Slavic languages for similar endings: start with Ukranian, then Belorussian, then go on to Polish (which is very conservative, and if there is any truly Slavic cognate to -alis, it would likely be in Polski), Slovak, or Czech. At this point, if you haven't found what you seek, chances are it won't be in the Southern Slavic languages either.