Why is Shakespeare called the founder of English language?
The English language has its foundation in many languages and, in Shakespeare's day, as ideas expanded and innovations increased, there were not enough words in the vocabulary to describe them. Shakespeare and others such as Christopher Marlowe and Edmund Spenser, added new words which they borrowed, developed, adapted or simply invented.
Shakespearean plays used few props and much of the drama came from the character portrayal. Shakespeare added depth and dimension to his characters through words by rearranging their order or apportioning some odd meaning to them- keeping the audience focused
to build the tension necessary to produce a riveting drama. (Reading Shakespeare, eNotes)
Other devices used by Shakespeare include his use of figurative language and comparison through metaphor such as in Macbeth - "There the grown serpent lies," as Macbeth refers to Fleance and simile still in Macbeth "Will plead like angels," and "pity, like a naked new-born babe."
Many Shakespearean words and phrases are used in everyday language without the speaker even being aware that he or she is quoting Shakespeare:
"the green-eyed monster", (Othello), "a bean feast" , " "some are born great, some achieve greatness....(Twelfth Night), "All the World's a stage, etc..."(As You Like It), "The Wheel is come full circle"(King Lear), "The course of true love never did run smooth" (A Midsummer Night's dream). There are many more.
According to "The Literary Encyclopedia" Shakespeare is the most widely read and most widely quoted writer in the history of the English-speaking world and
whose creative achievement has never been surpassed in any age. (eNotes)
thus his title as "founder" seems apt.