Hellenic, Italic, and Celtic. Were interlink together ancient languages which today still have similar …ie present day Scottish Gaelic
A French definition says that 'prehistory stops with the first written document'. By this definition, the Celts qualify as a prehistoric people. They were the first of the prehistoric peoples north of the Alps whose names were known to the Greek and Roman world, for they shared common features, including some linguistic similarities. The languages of the Celts belong to the great Indo-European family of languages, which also includes Anatolian, Hellenic, Italic, Illyrian, Slavonic, Baltic, Germanic, Armenian, Indo-Iranian, and Tocharian.
Like the other people associated with that region, the ancient Celts spoke a common Indo-European language taught to them by the Hellenic (Greeks) …..if I remember right?