左撇子 is the colloquial, everyday term. A more neutral term is 左利手 (zuǒlìshǒu). 右撇子 (yòupiězi) means right-handed, though it's less commonly said since right-handedness is the default.
culture
Historically in China, left-handedness was discouraged, and children were often trained to use their right hand. This attitude has relaxed considerably in modern times.
