From Nookipedia, the Animal Crossing wiki

Animalese is the default language the NPCs in the Animal Crossing series speak. Generally, each letter spoken is matched and synthesized with the basic sound of the letter in the language being played in, leading to mispronunciation of some words. (For instance, "Animal Crossing" in English would be pronounced "Ah-n-ih-m-ah-l c-r-o-s-s-ih-n-g".) In the Japanese versions, each kana syllable is matched with its proper sound, making it somewhat more legible to a Japanese speaker than the international versions. (どうぶつの森 would be "Do-u-bu-tsu no mo-ri".)

While much of Animalese is unintelligible, recurring phrases can be discerned, such as villager catchphrases and laughter. When numbers are spoken, they are pronounced clearly and legibly, similar to the sounds heard when writing a letter.

Animals that work in the town (Isabelle, Tom Nook, etc.) and traveling visitors (Gracie, Wendell, etc.) have distinct pitches to their Animalese. If text is quickly scrolled, the Animalese also speeds up, sounding more high-pitched. In addition, a villager's mood can affect their voice; happy villagers will speak in a higher pitch, while sad or angry villagers will have a lower one.

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.

The international releases of Animal Crossing reprogrammed the voice synthesizer based around the intricacies of Western languages, allowing for clearer pronunciation than in most later entries; the voices used are additionally pitched down compared to Doubutsu no Mori and Doubutsu no Mori+, a change that is reverted from Wild World onwards. Most later titles use the Japanese voice synthesizer across languages, resulting in Animalese sounding less intelligible in other languages compared to Animal Crossing.

Animalese in Wild World does not appear to be a proper voice synthesis, instead matching each letter to a random syllable. Because of this, it is entirely unintelligible, even with phrases that are clearly discerned in other games. This is likely due to the Nintendo DS's technical limitations, as proper voice synthesis returns in City Folk.

Prior to Animal Crossing: New Leaf, cranky villagers were the only villager personality type to have a unique pitch, having a deep, gravelly pitch. Lazy and jock villagers shared the same pitch, as well as all female personality types. Starting with New Leaf, all personality types have their own distinct pitches. Peppy and jock villagers now have a higher pitch than normal and lazy villagers respectively, whereas snooty villagers now have a lower pitch than normal villagers. Big sister and smug additionally have their own unique pitches as well, being lower than normal and lazy villagers, but higher than snooty and cranky villagers, respectively.

In Animal Crossing: Pocket Camp and Animal Crossing: New Horizons, Animalese works differently than in most previous games, reinstating the international release of Animal Crossing's method of refitting the synthesizer for different languages, allowing for clearer, more intelligible pronunciation. In addition, the species of a villager will slightly alter the pitch of their voice, which appears to be linked to the species' body size. For example, Dora (a mouse) has a higher pitch than Chevre (a goat), and Margie (an elephant) has a lower pitch than either, despite all three being normal villagers.

K.K. Slider and Kapp'n sing songs in their own variants of Animalese. While Kapp'n sounds very close to standard Animalese when singing, K.K.'s speech is entirely unique. It consists of the syllables "nah", "me", "oh", "now", and "queh", as well as howling, clicking, humming, and whistling. These variants of Animalese can also be heard on the airchecks for "Marine Song 2001" and "K.K. Robot Synth".

Bebebese or Silence can be spoken as an alternate language in the options in games prior to Animal Crossing: New Leaf.