The Cornish language, known in its own language as Kernewek, is one of the Brythonic group of Celtic languages which includes Welsh, Breton and, originally, Cumbrian. The Celtic languages of Scottish Gaelic, Irish and Manx are known as part of the separate Goidelic group.
In terms of similarity of Cornish to the other existing Celtic languages, it shares about 80% basic vocabulary with Breton, 75% with Welsh, 35% with Irish and 35% with Scots Gaelic. Welsh shares about 70% with Breton.”
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