Shakespeare lived during the late 1500s and early 1600s. This period is known as Early Modern English. For the most part people living today can understand Shakespeare’s work but some parts will need to be explained. But one thing that has changed a lot since then is pronunciation.
People have been painstakingly reconstructing the pronunciation of the language at that point through things like letters where people sometimes made spelling mistakes which reveal how they thought something should be spelled and also by looking at rhymes. Now that we know how the language at that time was spoken, people have been performing Shakespeare in the original pronunciation.