Guest, you need to get one thing straight before this discussion can go any further.

Gaelic is a separate language. It is a Celtic language once widespread in Scotland but now confined pretty much to the Western Isles. Scots is an Anglo Saxon language. Whether it can be considered a separate language from English or whether Scots and English are dialects of one another is an interesting point. Being of Anglo Scottish parentage, I am not sure what the answer is. Certainly "Broad Scots" is pretty much incomprehensible to people from the rest of Britain. But then so is Broad Geordie or Broad Yorkshire or Broad Devon. Also there are different dialects within Scotland. My mother was from Aberdeen and they certainly spoke differently from Edinburgh or Glasgow for example.

This then raises the question when does a dialect become a separate language?

I was reading a book about the Border Reivers recently and it had extensive quotes from writings of the time. While there were differences between the English and Scots in both spelling and grammar, with a little effort both were comprehensible to a modern English reader.