Why Does Meowth Speak?

One day, Meowth came across a female Meowth named Meowzie. She rejected him, saying that he was poor and that she preferred humans, so Meowth attempted to make himself more human-like to make her love him. Thus, he painstakingly taught himself to speak human language and walk upright like a human.

Is Meowth the only Pokémon that can talk?

Introduced early on in the Pokémon anime as part of the Team Rocket trio, Meowth is one of the only Pokémon who is able to speak to humans in their own language so consistently and articulately without relying on special abilities or circumstances. To be clear, only Team Rocket's Meowth seems to be able to do that.

Is talking Meowth rare?

They have failed to realize throughout the entirety of the show that they have in their possession the rarest Pokemon of all, a talking meowth.