In the ninth and tenth centuries the Vikings invaded Britain from Scandinavia and settled in large numbers. Their language, which we call Old Norse, was at least partly comprehensible to the English, who did not hesitate to take over hundreds of words from it: skirt, window, scrub, sky, give, hit, kick, scatter, scrape, skill, scowl, score, fellow, want, skin, knife, law, happy, ugly, wrong and even the pronouns they and them.
Not long time ago there was a striking example of the extent to which English has diverged: a television company put out a programme filmed in the English city of Newcastle, where the local variety of English is famously divergent and difficult, and the televised version was accompanied by English subtitles!
The likelihood is that any English-speaking skier has more words for different types of snow than any inhabitant of Alaska or Greenland.
I recall that, the first time I met a Geordie speaker, it was some days before I could understand a single word he was saying.
The grammar of a language is simply the way it combines smaller elements (such as words) into larger elements (such as sentences).
