Chaucer primarily used the Middle English dialect known as Middle English London, which was spoken in the east midlands region of England during his time. This dialect influenced the development of Modern English.
Early Modern English started around 1500. For reference, Shakespeare is in Early Modern English; Chaucer is in the London dialect of Middle English.
The common people in Mediaeval England spoke Middle English, which eventually evolved into Early Modern English and then Modern English. Middle English started around the 12th century and included dialects such as Kentish, West Midlands, and East Midlands, as well as the London dialect that eventually became dominant.
Modern English evolved from Middle English, which itself developed from Old English. This process occurred over centuries through various influences, such as the Norman Conquest and interactions with other languages.
To simplify a complex subject, the East Midland dialect of Old English became the dominant dialect as it replaced the conservative (as in, little influenced by Scandinavians from the north) Kentish dialect of London. The East Midland dialect had lost many of the inflections of Old English, and after the Norman invasion of 1066, gradually evolved (in part due to a further simplification of inflections as Norman French eventually learned English) with additions from Latin (sometimes from Greek) and French (of various dalects).
Shakespeare wrote in modern English, in the dialect called Early Modern English.
If anything, it came from 70's 'culture shock', not from any regional British dialect.
"Middle English" is a subset of English. Middle English is the type of English spoken in Chaucer's time, as in _The Canterbury Tales_. English is a language as a whole, but over time, the dialect has changed from Old English, the dialect spoken in _Beowulf_, to Middle English, the dialect spoken in Chaucer's time, in _The Canterbury Tales_, to Modern English, the dialect spoken in Shakespeare's time, in _Hamlet_, to today's English, the dialect I'm writing in right now.
Sae is the the Old English ( West Saxon) form of "sea." There is also the modern English word sae, which is the Anglic dialect form of "so."
Modern English is a descendant of Middle English, which in turn evolved from Old English. The development of Modern English can be traced back to the 15th century when the language underwent significant changes in vocabulary, grammar, and pronunciation.
Modern English comes immediately from Middle English, the language of Chaucer. That derived from Old English or Anglo-Saxon, the language of Beowulf. That language, little more than a Germanic dialect, derived from Common Germanic, the common language of all Germanic languages (Dutch, Friese, German, Scandinavian...).
Modern English, the same language I am writing in and you are reading. It is a different dialect called Elizabethan or Early Modern, but the same language, easily comprehensible by English-speakers today.