From Nookipedia, the Animal Crossing wiki
Animalese is the default language the NPCs in Animal Crossing series speak. Each letter spoken is stated to synthesize the basic sound of a letter, leading to mispronounciation of some words. (i.e. "Animal Crossing" would be pronounced "Ah-n-ih-m-ah-l c-r-o-s-s-ih-n-g"). When villagers say numbers, they will talk rather clearly, like when the player is typing a letter. The name of the player and the name of the town can be clearly discerned as well, although they may also be mispronounced depending on the way each letter of the word is said in Animalese. Laughing and similar sounds are also discernible. However, much of Animalese is mostly unintelligible, but some phrases can be heard.
Different personalities (such as Cranky or Snooty), animals that work in the town (ex: Pelly, Tom Nook) and 1-day visitors to the town (Gracie, Wendell, etc.) will have different pitches to Animalese. Different characters will have higher or lower voices. If text is quickly scrolled, the Animalese also speeds up, sounding more high-pitched. Also, happy, sad, or angry villagers will have a different pitch to Animalese. Furthermore, the sound of Animalese differs slightly in each game. In Animal Crossing and Animal Crossing: New Leaf it is spoken very quickly, while in Animal Crossing: Wild World and Animal Crossing: City Folk it is spoken slightly more slowly.