The highest mountain in Yorkshire is Pen-y-ghent. What language is this?

Welsh.

What we now call Welsh was the native language of much of Great Britain before the Anglo-Saxon invasions.

Surely it is actually Celtic.

Ghent is a corruption of "cant."

A prominent natural feature used as a boundary point in the eastern section of the boundary is Pen-y-ghent. The name comprises two British place-name elements: pen 'top, head, end' and cant, which would suggest this 1307 boundary point, also on the boundary of the former British district of Craven, existed several centuries earlier.

http://www.yorkshireguides.com/pen_y_ghent.html

Firstly there is no such thing as a Celtic or ancient British language. The Celtic tribes, including the Belga and those from Iberia, divided on these islands eons ago into the Goidelics who developed Irish and Pictish Gaelic, and the Brithonics whose language developed into Welsh. At the time of the Roman conquest Welsh was spoken from the middle of Scotland to the coast of Kent. In the words "pen y ghent," the ghent has been corrupted from gwynt which means wind. Pen y ghent originally meant "a windy summit." Pen can mean head, top, or even hill.

To reinforce the argument there is little doubt that Glasgow has been corrupted from "glas y glo" which means "blue coal" and Welsh miners were probably digging it there about 4,000 years ago.

Incidentally, Welsh is not the oldest language in Europe, that accolade belongs to the Basques. There is still no real knowledge of its source. The Welsh (which includes the Cornish and the Bretons, the three are the same) have close cousins with the Walloons in Belgium, from whence comes the word Wales. Welsh for the Welsh is "Y Cymri." So please no more talk of ancient Britons or ancient Celts, come out of denial and just call them what they were, Welsh.

To be honest it doesn't matter to me. It could be Klingon for all I care. I only posted what I found and ...

The Brigantes, a British north-western Celtic tribe, occupied much of the Dales centuries before the arrival of the Romans and sometime after. There were two main dialects of the Celtic language - British in England and Wales and Gaelic in Ireland - and had a small influence in the area in which it was spoken. This British language can be found in the names of many hills and rivers, such as Pen-y-ghent, Penhill and Pendle where penno means hill, and Nidd ('brilliant'), Wharfe ('winding'), and Ure ('strong'). The Romans had little influence on the place-names of this remote area of the empire and many Celtic names disappeared with the arrival of the Anglo-Saxons in the 7th and 8th centuries and the Vikings.

http://homes.chass.utoronto.ca/~cpercy/courses/6361Lovis.htm

Pen-y-ghent is not the highst mountain in Yorkshire, it is 694m (2277 ft), lower than Whernside 736m (2415 ft) and Ingleborough 723m (2372 ft). The language is thought to be Cumbric which is a Brythonic Celtic language like Welsh and Cornish, spoken up into southern Scotland but how different it was from Welsh is not known as it is now extinct.

https://en.wikipedia.org/wiki/Yorkshire_three_peaks

The mountains of Whernside, Ingleborough, and Pen-y-ghent are collectively known as the (Yorkshire) Three Peaks. The peaks, which form part of the Pennine range, encircle the head of the valley of the River Ribble, in the Yorkshire Dales National Park in the North of England.

[Added reference - McG]

Pen-y-ghent is originally Welsh. It was common up until the 1950's to hear farmers in Yorkshire to still count sheep in Welsh, un, dau, tri. And I didn't know until recently Dover comes from the Welsh Dwfr (hamlet by the water) and Malvern Hills (Moelfryn - bare hills). Interesting.