https://www.theatlantic.com/international/archive/2016/01/di...
It made an interesting point about English:
"English tempts one with a tidy dialect-language distinction based on “intelligibility”...But because of quirks of its history, English happens to lack very close relatives, and the intelligibility standard doesn’t apply consistently beyond it. Worldwide, some mutually understandable ways of speaking, which one might think of as “dialects” of one language, are actually treated as separate languages. At the same time, some mutually incomprehensible tongues an outsider might view as separate “languages” are thought of locally as dialects."
This is spot on. The first thing I did after reading the article was go to Scots Wikipedia. I could read the articles pretty well after a minute, since there seems to be a nearly one-to-one mapping between the Scots words and English words, and so I thought "this isn't a language." The grammar was different than standard english, but similar to the way some southerners talk. But had I grown up speaking another language maybe I'd have a different instinct about whether that intelligibility made it a language. Moreover, says something I chose written language for deciding whether it's a language or not: all english speakers are used to not being able to understand spoken english from other places and classes.
In the end, I suppose the whole difference is socially constructed and involves politics mixed with what people regard as common sense.
Random sample ("featured article") from the scots wikipedia: "The testicle (frae Laitin testiculus, diminutive o testis, meanin "witness" o virility, plural testes) is the male gonad in ainimals. Lik the ovaries tae which they are homologous, testes are components o baith the reproductive seestem an the endocrine seestem."