According to the Wiki page the Gaelic name for the Scottish Lowlands can be translated as, "the place of the foreigner". I'm wondering which foreigners they are referring to. Also, if this actually refers to Celts then who are the native people that created this name?
BTW, if you have a good answer you may want to add to the Wiki page so that others may find this information easier.
The word 'Galldachd' for the lowlands arises from the Old Irish 'gall' for 'foreigner' which came in turn from the Latin word 'gallus' for a Gaul. http://www.wordsense.eu/Gall/#Old_Irish.
The Gaels called (indeed call) their linguistically and culturally Gaelic part of Scotland the Gàidhealtachd, usually translated as 'Gaeldom'. This cultural way of viewing the world gives a hint to what the Gaels meant when they said 'foreigners' ... they basically meant 'land of the non Gaels'. 'Foreigners' was not meant necessarily as any sort of denigration - it was just a simple statement of cultural and linguistic fact.
The Irish word 'galldacht' has a closely related sense (although not identical) of the English, English speakers and the region of the Irish Pale, and therefore 'Galldachd' also had or came to have a sense of 'a region that is culturally English' - again meant as a simple reflection of the shared language and culture of lowland Scotland and England at that time, and not as any kind of denigration or diminution of Scottishness.
In the years when these terms developed, there was no nation of Scotland, and Gaelic Scotland had little in common with the part of modern Scotland where people spoke the precursor dialects of Middle Scots. Even after the political entity of Scotland came into existence, the highlands and islands remained strongly distinct, and weakly controlled by the lowland Scots monarchy. A long tradition of antipathy between the two cultural regions meant that there would have been little motivation to ever stop calling the lowlands by a word that tended to underline the separation between the peoples.
Well, the obvious conclusion would be that this is a reference to the historical fact that the lowlands tended to have a lot more non-Gaelic speakers living in them.
Of course, place names can be tricky, so it isn't always wise to go with the obvious. They tend to be very "conservative", in that they can be the oldest words in use in a language, or even predate the language itself. Often times new settlers in an area will borrow an existing place name from the existing residents, and then bash it into some kind of slightly different form that is easier for them to pronounce, or has some plausible local meaning. So, in the absence of any evidence to its origins, it would be quite possible for it to have been an old Pictish word that the Gaels(Scotts) took up when they took over the highlands sometime around the 10th century, and then slightly transformed so that it actually meant something in Gaelic.
