The Celtic languages (usually pronounced /ˈkɛltɪk/ but sometimes /ˈsɛltɪk/) are descended from Proto-Celtic, or "Common Celtic"; a branch of the greater Indo-European language family. The term "Celtic" was first used to describe this language group by Edward Lhuyd in 1707.
Modern Celtic languages are mostly spoken on the north-western edge of Europe, notably in Ireland, Scotland, Wales, Brittany, Cornwall, and the Isle of Man, and can be found spoken on Cape Breton Island. There are also a substantial number of Welsh speakers in the Patagonia area of Argentina. Some people speak Celtic languages in the other Celtic diaspora areas of the United States, Canada, Australia, and New Zealand. In all these areas, the Celtic languages are now only spoken by minorities though there are continuing efforts at revitalisation. Welsh is the only Celtic language not classified as "endangered" by UNESCO.
During the 1st millennium BC, they were spoken across much of Europe, in the Iberian Peninsula, from the Atlantic and North Sea coastlines, up to the Rhine valley and down the Danube valley to the Black Sea, the northern Balkan Peninsula and in central Asia Minor. The spread to Cape Breton and Patagonia occurred in modern times. Wikipedia