Like many others, the works of William Shakespeare are subject to obsolescence as time goes on. Consider slang from just forty years ago in the 1970s, and how it has become entirely uncommon, and it is easy to see how slang from the 16th century could be almost in another language.
For example, "Fie!" as an expression of astonishment or shock; this appears in many of Shakespeare's works, but is unheard-of today; it has been replaced by various obscenities and vocal exclamations.
Similarly, "Hie!" as a reproach to hurry up or move faster; this could be read today as "get the lead out!" or "move it!"
The word "Foredone," meaning to kill or finish, appears often in Shakespeare's sonnets. Today, the sentence "All with weary task fordone" from A Midsummer Night's Dream would be written "All wearying tasks completed," or "Having finished all his exhausting work."
"Avaunt!" is common in Shakespeare as well, and means "back away!" This could also be written "bugger off," if one resides in England.
There are many, many other Elizabethan slang words and phrases that have all-but vanished today.