Alex Richards
Donor
https://www.ethnologue.com/language/sco
https://www.ethnologue.com/language/gla
90k Scots speakers, with 1.5m people who have it as a second language. That's our of a population of 5.3 million (ie 28%).
Scots is not really mutually intelligible with English (except at the "ridiculously strong accent" level; imagine someone from the US Deep South trying to understand a Geordie), although in written form, a decent language scholar could work it out.
But it's Lowland culture, hence if Scotland decides to push her own language rather than English they're going to go for that rather than Scots Gaelic.