The Vietnamese phrase "buông miệng" literally translates to "to let the mouth go" in English. It is often used in a colloquial context to mean "to speak" or "to open one's mouth to say something." However, it usually carries a negative connotation, implying that the person is speaking thoughtlessly or saying inappropriate things.
"Buông miệng" is a useful phrase to describe someone who speaks without thinking, especially in a negative or inappropriate way.