Due to the presence of Scottish Gaelic, Scotland is generally considered a Celtic country, but do you think this can be challenged? For one thing, the vast majority of Scots are lowlanders, and they’re been speaking English for a very very long time. Indeed longer than some parts of England. Cornish is still spoken today after all, and in Cumbria they were speaking Welsh as recently as 8 or 9 centuries ago.
The Shetlands and Orkneys spoke a language called Norn which is very close to Danish and Norwegian up until a few centuries ago too. Would it be fair to say Scottish origins are complicated?
I have trouble accepting mono-culturalism in general. As you say, Scotland is usually considered a Celtic country but some prefer to highlight other origins, such as the Nordic ones. When I think of my home country (Spain), I get the same feeling. It is generally seen as a Mediterranean country but only about 1/3 of the population lives in the Mediterranean. The Lusitanian, Basque or even Arabic backgrounds of the country are still very much present.
So in answer to your question: yes, Scottish origins are terribly complicated. I would argue that pretty much every country’s origins are. At the end of the day, isn’t every nation a combination of cultures? In fact, how many mono-cultural states do we know?
If you require the Celtic language to be the majority language, there are no Celtic countries. All of Scotland spoke a Celtic language (except possibly Shetland, and of course as far as we can tell) about 2000 years ago. Of course, so did all of England and most of France and much of Spain. So when we say “Celtic country,” all we mean is that there is (a) a historic presence of a Celtic language, and (b) still speakers of that language.
It is doubtful if Celtic speech persisted much longer in Cumbria than it did on the Scottish side of the Cumbrian border. The shift to English probably began in the 11th century in both places, and was probably complete within about 200 years.
It’s not a zero-sum game. Nobody in their right mind would deny that Germanic speakers have been in all of the Celtic countries from the 10th century at the latest, with a continuous presence in all of them except Brittany. In that sense, you could also call them Germanic countries.
If you want to look at it from the time English law replaced Celtic legal systems, Scotland arguably kept Celtic legal culture alive longer than anyone, since the Kingdom of Scotland arose out of the Gaelic-speaking part of the country, unlike the other Celtic countries which were all conquered or formally incorporated into the English and French states.