OK, we’ll be straight with you: in its original Middle English, Sir Gawain and the Green Knight
is pretty darn near impossible to read, even for people who have a pretty easy time with, say, Chaucer. Why? Well, at the time the poem was written, English was not the same everywhere it was spoken. Without the dialect mixing brought on by TV, radio, telephones, the internet, or even the printing press, little geographical "pockets" could have their own distinct versions of English. Sir Gawain and the Green Knight was written in northwestern England, close to Wales, in a dialect called North West Midlands.
With the advent of the printing press, Chaucer’s London English became the standard form of English that was passed down and is the form closest to what we speak today. By contrast, the North West Midlands, unlucky enough to be far from a center of printing, did not get passed down, so that today, nobody except specialists who study it their whole lives can really understand it that easily.
All is not lost, though: many eminent medievalists, including J.R.R. Tolkien, have rendered Sir Gawain into modern English translations, many of them quite beautiful. But since there’s no substitute for the original, we recommend a facing-page translation with the Middle English side-by-side with the modern. That way, you can understand the poem and learn cool North West Midlands words like burne (for man) and blonk (for horse).