Scots language history
Cumbric and English were minority languages in the kingdom of the Scots/Gaels and confined to the Clyde valley and Lothian by the 11th century. The Scots language was Gaelic at this time as it was the language of the Scots (lingua Scottorum) who had founded the Scots kindom. Furthermore, Pictish and Gaelic may have been a lot more fluid than is often assumed as they along with Cumbric had all been one language a few centuries earlier and this Common Celtic had been spoken across Britain and Ireland at the time when the Romans arrived. Peter Schrijver believes it is this Roman presence which accounts for the rapid changes in both Goidelic and Brythonic which took place between the fifth and seventh centuries and that before then, they had been a dialect continuum, which may explain how Argyle has been autochtonous from Ireland and yet Gaelic at a time before the Gaels/Scots brought their version of Celtic Eastwards across Northern Britain and arguibly back engineered Pictish dialects to a common language that had been the case in the first century ce.On pages 79 to 80 of his book "Language Contact and the Origins of the Germanic Languages", Professor Peter Schrijver writes: " The closest cognate of Irish is British Celtic, or rather Highland British Celtic, the ancestor of Welsh, Cornish, and Breton that was spoken in the west and north of Britain. Although on the face of it the Old Irish of the seventh century and Old Welsh and Breton of the eighth century look very different from one another, almost all of the differences between them had arisen in a relatively short period between the ﬁfth and seventh centuries AD, when masses of sound changes affected both languages. In fact, during the Roman period Irish and British Celtic must have been so similar that Celtic speakers on either side of the Irish Sea had little difﬁculty in understanding one another’s language. The earliest datable linguistic development that was not shared between Irish and British is the development of the Proto-Celtic diphthong * ai to * ɛ̄ (as in English bed but long), which affected British Celtic but not Irish, probably at some point during the later ﬁrst century AD at the earliest. Before this happened, Irish and British Celtic were not just mutually comprehensible dialects; they were indistinguishable from one another."