Btw, gaelic (the ancient language native to scotland) is pronounced with a
broad 'ah' sound, not 'ay' sound as in 'pay' - so it sounds like "gahlic".
Also, yes most scots would consider themselves to speak English, however it
never used to be like that. Historically, scotland spoke gaelic in the
highlands and "early scots" in the lowland where most of the people are.
Scots is a Germanic language sister to english. After the uk was formed,
due to control from England, English was the language of education and the
upper class. As a result, the people of scotland speak an anglicised
diluted version of scots and retain the accent and dialect words of the
past: speech can be considered a continuum between 'Scottish English'
(standard English which sounds scottish) and 'broad scots' (many people
still speak heavily in dialect, these words are not slang!!)
One of the reasons the accent and dialects vary so much is because scots
was never made the national language and hence never standardised and
homogenised like the English spoken in some parts of America. Also the
reasons highlanders don't understand lowlanders is because the highlanders
who no longer speak gaelic usually speak a more standard form of English-
they never spoke scots