I haven't seen the show, do you know if it was based in the Highlands or the Lowlands?

The Lowlands was always a location where there was more of a crossover between English and Scottish Gaelic, but in the 18th century the Highlands would have been more or less exclusively Gaelic.

The 19th century brought about a rapid shift from Gaelic to English across the country, but again in the Lowlands it happened a lot quicker and more easily than in the Highlands, so there would have been a lot more bilingual people.

To jump on this at what point was scots completely abandoned in favor of english by the average scotsman?