Middle to modern English (Or early modern/transitional modern for the pedants...). Chaucer was middle English, fairly incomprehensable, and Old English was virtually germanic, being comprised of bits of norse, saxon, jute and friesland dialects, combined with a bit of celtish and Latin.
Shakespeare is Terry Pratchett by comparison....
"Modern English is the form of the English language spoken since the great vowel shift, completed in roughly 1550.
Despite some differences in vocabulary, material from the early 17th century, such as the works of William Shakespeare and the King James Bible, is considered to be in Modern English, or more specifically, they are referred to as Early Modern English, and most people who are fluent in the English of the early 21st century can read these books with little difficulty."