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.
Wales
In his 1707 work "Archaeologia Britannica" Edward Lhuyd, keeper of the Ashmolean Museum, noted the similarity between the two Celtic language families: Brythonic or P–Celtic (Breton, Cornish and Welsh); and Goidelic or Q–Celtic (Irish, Manx and Scottish Gaelic). He argued that the Brythonic languages originated in Gaul (France) and that the Goidelic languages originated in the Iberian Peninsula. Lhuyd concluded that as the languages had been of Celtic origin, the people who spoke those languages were Celts. (According to a more recent hypothesis, also widely embraced today, Goidelic and Brythonic languages, collectively known as Insular Celtic languages, evolved together for some time separately from Continental Celtic languages such as Gaulish and Celtiberian.) From the 18th century, the peoples of Brittany, Cornwall, Ireland, Isle of Man, Scotland and Wales were known increasingly as Celts, and they are regarded as the modern Celtic nations today.