doesn't know what they're talking about
Es un chico, no sabe lo que dice.
He's a kid, he doesn't know what he's saying.
— Adiós, muchachos (1987)
Listen, he doesn't know what he's saying.
Escucha, él no sabe lo que dice.
Listen, he doesn't know what he's talking about.
The poor thing doesn’t know what she’s saying.
— Mujeres al borde de un ataque de nervios (1988)
People don't know what they're saying.
— El bueno, el feo y el malo (1966)
Bebió demasiado, no sabe lo que dice.
He drank too much; he doesn't know what he's saying.
Quien dice estas cosas no sabe lo que dice.
Whoever says these things doesn’t know what they’re talking about.