Dialect of A or new language B?

A. Even when there is no continuum of this kind, the question of whether one speech variety is a dialect of one language or a new language entirely is often undecidable.

B. Scots English can test the comprehension of an English speaker. Consider that auld lang syne means old long since. But hearing Scots spoken at speed in casual situations, an English speaker is often confronted with what feels like an ill-tuned radio signal. This is an experience typical of speakers of most languages: English is unique in how few speech varieties straddle the line between it and other languages.