Putting it all together, 喋喋不休 literally means “chatter-chatter-not-stop.” The structure is simple, direct, and paints a very clear picture of someone talking without a break.
In Chinese culture, there's often a high value placed on thoughtful, concise, and meaningful speech. Silence is not always seen as awkward; it can signify wisdom, contemplation, and respect. Therefore, someone who talks 喋喋不休 can be perceived as lacking substance, being frivolous, or even disrupting social harmony (和谐, héxié). A good Western comparison is the term “to ramble on” or “to be a motor-mouth,” but 喋喋不休 carries a stronger weight of annoyance. While an English speaker might call a friend a “chatterbox” with some affection, describing someone as 喋喋不休 is a clear criticism. It implies that the talking is not only excessive but also grating and unwelcome, infringing upon the listener's sense of peace and quiet. This idiom is a powerful tool for expressing exasperation with someone who doesn't know when to stop talking.
This idiom is very common in modern spoken and written Chinese. It's a go-to phrase for complaining about someone's talking habits.