If you tally up Scotland, Wales and Ireland, that’s bare minimum 2/3rds Celt. I’d say you’re on solid ground there.
CC
Northwestern France is the area known as Brittany. The language spoken there is Breton. It is a Brythonic language in the group with Welsh/Cornish/Breton. The Goidelic languages are Irish Gaelic, Scot's Gaelic and Manx. I have sufficient facility with French and Welsh that Breton is intelligible as a regional mix of both languages.