A well known "Scottish" song is The Broom of the Cowdenknowes but it's an English song written as what a Scottish song would sound like. (see Child Ballads) Scots has changed over the years, Robert Burns and his verses are in an almost unknown dialect in modern Scotland, although some 40-50 years ago they were readly understood, and my Grannie a further 60-70 years before that spoke very much in the Burns style.