How the English Failed to Stamp Out the Scots Languagehttps://www.atlasobscura.com/articles/scots-language
Scots arrived in what is now Scotland sometime around the sixth century. Before then, Scotland wasn’t called Scotland, and wasn’t unified in any real way, least of all linguistically. It was less a kingdom than an area encompassing several different kingdoms, each of which would have thought itself sovereign—the Picts, the Gaels, the Britons, even some Norsemen. In the northern reaches, including the island chains of the Orkneys and the Shetlands, a version of Norwegian was spoken. In the west, it was a Gaelic language, related to Irish Gaelic. In the southwest, the people spoke a Brythonic language, in the same family as Welsh. The northeasterners spoke Pictish, which is one of the great mysterious extinct languages of Europe; nobody really knows anything about what it was.
The Anglian people, who were Germanic, started moving northward through England from the end of the Roman Empire’s influence in England in the fourth century. By the sixth, they started moving up through the northern reaches of England and into the southern parts of Scotland. Scotland and England always had a pretty firm border, with some forbidding hills and land separating the two parts of the island. But the Anglians came through, and as they had in England, began to spread a version of their own Germanic language throughout southern Scotland.
I have a fair amount of Scottish (and Irish) ancestors (Skye, Hebrides, Argyll/Inverness and Sligo), as well as southern English (Cornwall, Devon, Somerset, Dorest, Wiltshire, Hampshire/Isle of Wight, and London/Middlesex) on my mother's side and mostly Lancashire/Yorkshire and Scottish/Irish on my father's side. Still tracing links to the past.