History of Scottish Gaelic
All surviving dialects are Highland and/or Hebridean dialects. Dialects of Lowland Gaelic have become defunct since the demise of Galwegian Gaelic, originally spoken in Galloway, which seems to have been the last Lowland dialect and which survived into the Modern Period. By the 18th century Lowland Gaelic had been largely replaced by Lowland Scots across much of Lowland Scotland. According to a reference in "The Carrick Covenanters " by James Crichton, the last place in the Lowlands where Scottish Gaelic was still spoken was the village of Barr in Carrick: only a few miles inland to the east of Girvan, but at one time very isolated. Crichton gives neither date nor details.
Celts
Insular Celtic culture diversified into that of the Gaels (Irish, Scottish and Manx) and the Celtic Britons (Welsh, Cornish, and Bretons) of the medieval and modern periods. A modern Celtic identity was constructed as part of the Romanticist Celtic Revival in Great Britain, Ireland, and other European territories, such as Portugal and Spanish Galicia. Today, Irish, Scottish Gaelic, Welsh, and Breton are still spoken in parts of their historical territories, and Cornish and Manx are undergoing a revival.