Frisian is often cited as the language that is closest to English, but Scots is actually closer (i.e. has a higher degree of mutual intelligibility with English). Not Scottish English, which is a variety of English, or Scottish Gaelic, which is actually a Celtic rather than a Germanic language, but Lowland Scots.
There are just over 100,000 native speakers and it is classified as a traditional language by the Scottish government and a regional or minority language by the European Charter for Regional or Minority Languages.
Here is a lecture in Scots about the history of the Scots language. How much can you understand?
Dr. Wagner has a PhD in Linguistics and is dedicated to learning and teaching languages online and abroad. She has studied in Quebec and Australia, taught English in France, and is currently based in the US.