Alot of south american natives practised cannibalism when both the portuguese and the spaniards got there...and they probably still do in the isolated(and still unexplored areas) of the amazon basin. Actually head hunters (which also practised ritual cannibalism) were still doing it some 30 years ago.

Human sacrifices were common among the celts and other ppl's...who knows if a couple of druids didnt have a snack of human flesh from time to time to gain the favour of the Gods. :)

About the colonization of Ireland by ppl from the Iberian Peninsula...thats perfectly logic for me. Not only because there was a somewhat visible commerce with nowadays Britanny (one of the areas occupied by the Venetii if i am not mistaken) but also because there were exchanges from Britanny to the british isles. So i guess it makes sense, those ppl could probably understood themselves well...can´t see why not. I guess we are used to think that tribes and villages were simply isolated from the rest of the world...and probably alot of them were...but the sea and rivers are a very good highway.