From Kook Science

Pictish (Pechtish, Cruithnis) is a now-extinct language, formerly spoken by the Picts from the late Iron Age, prior to the conquest or conversion during the Early Middle Ages of their traditional lands, Pictland (Pictavia), including the Kingdom of Fortriu, into the Gaelic-speaking Kingdom of Alba (a.k.a. Scotland). All evidence regarding the language, including its origins, draws from certain surviving toponyms and possible loanwords incorporated into Gaelic, as there is no proved written record of the language extant, though it has been proposed that the Newton Stone and Lunnasting Stone represent surviving examples of the Pictish language.