Donald Duck’s distinctive speaking style is a type of alaryngeal speech – it is made without using your voice box.

Half of the consonants and all of the vowels (in English, at least) are made using your larynx, or voice box. Inside the larynx, two flaps of tissue called the vocal chords vibrate as we push air between them. That vibration is our voice. Muscles tighten or loosen these flaps, and that changes the pitch of the “voicing” sound; we move our jaw, lips, and tongue around to modify that voice and produce words.
As I mentioned a couple of years ago in the post on the International Phonetic Alphabet, consonants can be divided into “voiced” sounds that are produced with laryngeal vibration (/b/, /z/, /g/, etc.) and “voiceless” sounds that do not use the vibration (/p/, /s/, /k/, etc.). Human speech depends on the larynx. But not always It is possible to bypass the larynx entirely, and one of the most famous perpetrators of this is Donald Duck.
People who have lost their larynx from injury or disease will sometimes create a similar voicing sound with other parts of their throat: esophageal speech and pharyngeal speech. Burp speech is esophageal, for example. But Donald Duck speech is entirely created inside the mouth.
First, push some air between your cheek and your jaw. Then push that air out with your cheek muscles. The resulting rough vibration can substitute for your larynx – and boom, you’re talking like Donald Duck. The creator of this voice was Clarence Nash, pictured above with some mighty powerful cheeks. He originally thought it sounded like a nervous baby goat. It was Walt Disney who thought it sounded like a duck. And so, in 1934, Donald’s “buccal speech” (cheek speech) became permanently connected to Donald Duck.