Can you please speak Chinese and how do you pronounce it in English?

Please speak Chinese.

Speak means speaking without emphasizing the content of the speech, so it is often used as an intransitive verb. If used as a transitive verb, it can mean speaking a certain language. .

Say means to speak, emphasizing the content of the speech, and is often used as a transitive verb.

Tell is to tell, usually controlling an indirect object and a direct object, and is used as a dative verb.