celtic is what nationality
(Akin to the later spread of Latin as a lingua franca and the more recent spread of English.). Celtic is a member of the Indo-European language family. A form of Celtic could well be one of the earlier manifestations of the Indo-European tongues. Certainly in the centuries post 1000 BC Celtic in one or other of its two main forms spread from Scotland to Turkey, Iberia to Switzerland. Roman conquests particularly post 100 BC eliminated the Celtic tongue pretty effectively from areas such as Spain, Portugal, France, England.