The idea of mutual intelligibility is interesting, yet due to how the Urnfield culture that spoke proto Celtic just north of the Italian peninsula (and inside modern Bologna, Venice, and Milan) how intelligible could these languages have been? Some interesting cognates being,-
Léigh - leggere (to read)
Can - cantare (to sing)
Creid - credere (to believe)
Corp - corpo (body)
(A More Expanded list of Cognates, https://forum.duolingo.com/comment/8156398/Interesting-similarities-between-Irish-and-Italian-words)