Chatter is learned by 1 species by level

Effect, in PokéAPI's words

“Has a higher chance to confuse the target when the recorded sound is louder.”

Who learns it

1 species in all, 8 of 10 games shown

Brilliant Diamond and Shining Pearl: 1 species

Species	Method	Level
Chatot	Level up	1, 21

Ultra Sun and Ultra Moon: 1 species

Species	Method	Level
Chatot	Level up	1, 21

Sun and Moon: 1 species

Species	Method	Level
Chatot	Level up	1, 21

Omega Ruby and Alpha Sapphire: 1 species

Species	Method	Level
Chatot	Level up	1, 21

X and Y: 1 species

Species	Method	Level
Chatot	Level up	1, 21

Black 2 and White 2: 1 species

Species	Method	Level
Chatot	Level up	21

Black and White: 1 species

Species	Method	Level
Chatot	Level up	21

HeartGold and SoulSilver: 1 species

Species	Method	Level
Chatot	Level up	21

Changed over time

One change since Generation IV

1. Through Gen VPower 6065 from X and Y, Generation VI