To avoid confusion, I'll refer the English-based Scots as English and the Gaelic one as Celtic.

I'm watching been Outlander TV series for the past week. It's set in 18th century Scotland. A fair amount of the dialogue is in Celtic. I'd like to think that the producers made a good effort in trying to make it historically accurate, at least on the Scottish culture side of things.

What bugs me though is that everyone in the show is bilingual. They can speak both English and Celtic. That can't be right. It's as if they just forcefully include some Celtic into dialogue to make it romantic or some sort and have it in English to make actual viewers understand.

I'm not quite familiar with Scot history but aren't they suppose to be only proficient in one language? I mean, probably at one point in history, Scots spoke Celtic but in another era, they would speaking in english. If Celtic's the language, then I would expect only the Laird and a few of his higher ranked men to be capable of speaking it.

So which language was used by common folk in 18th century?