At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
is this in English ?
Fustian is heavy twilled fabric, more or less like blue jeans. A jupon is a long coat, and a habergeon is a sleeveless coat of mail. Here we're told essentially that he's wearing plain jeans and plain coat, that's been stained by his chain-mail (I guess with rust). So he's dressed plainly, and his clothes are designed to be simple and long-wearing, and yet are nevertheless worn with his travels (detailed in the lines above), so we it seems he is, despite his high rank (of knight) a humble man, not given to showy dressing, and moreover one who takes his vocation (being a knight) seriously, and bears the marks of wear of a serious fighter (the wear on his clothes). Presumably Chaucer is trying to contrast him with a knight who uses his high position to wear expensive, flashy clothing, and who takes such care of his person and his clothes that they are never stained or worn -- who doesn't take his responsibilities as a knight seriously.