One thing we have to remember is that since the Dark Ages began (535 AD, otherwise nice Spring day that really went downhill fast) ONE MAIN Division of the Celtic languages totally disappeared, and numerous dialects bellied up. Even Galician (the language of the Milesians who invaded Scota ~ now Ireland ~ about 700 BC) disappeared in the 1600s and was replaced with THREE KINDS of Spanish.
Pict or Latin “Picti” is from the Latin for “painted,” I think.