Why do Chinese novel characters speak in idioms?

A villain corners the hero and says something about a mantis stalking a cicada while an oriole waits behind. The hero replies that a frog at the bottom of a well cannot see the sky. Neither of them is talking about animals. Chinese idioms in translated novels arrive like this, four words at a time, and a reader who doesn't know the code wonders why everyone in the jianghu talks like a fortune cookie.

What a chengyu is

A 成语 (chéng yǔ) is a set phrase, almost always four characters, that compresses a story or a line of classical text into a single unit. There are thousands, and educated Chinese speakers use them constantly. 井底之蛙, the frog at the bottom of the well, means a narrow-minded person. 画蛇添足, drawing legs on a snake, means ruining something by overdoing it. 螳螂捕蝉, the mantis stalks the cicada, means being so focused on your prey that you miss your own predator. Each one is a whole fable in four syllables, and a fluent speaker hears the meaning instantly, the way an English speaker hears "sour grapes" without picturing a fox.

What they do in the source

In fiction, chengyu are how characters sound clever. A scholar uses them to show learning, a villain uses them to be sinister without being crude, and a sect elder uses them to lecture. Web novel authors also use them in narration as a kind of shorthand: instead of describing a crowd's reaction, the narrator says they were 目瞪口呆, eyes wide and mouth agape, and moves on. Some authors stack them, and a fight scene can have a chengyu in every sentence, each one a tiny classical quotation.

Tone rides on them too. A character who uses a famous chengyu incorrectly is being shown up as half-educated. A character who twists one on purpose is being witty. And characters can duel with them, answering one idiom with another that reverses it, which is what the mantis and the frog were doing above.

How translators handle it

Literal: the mantis and the cicada, the frog in the well. Fan translations love this, and it's why English readers know some chengyu at all. The reader gets the image and a bit of the culture, and with a footnote, the fable. What you pay is speed, and strangeness: a phrase that a Chinese reader took in without noticing becomes a small riddle, and a paragraph with four of them turns into a menagerie.

Equivalent: swap in an English idiom that means the same thing. The frog in the well becomes "he's never seen past his own fence"; drawing legs on a snake becomes "gilding the lily." This reads smoothly and keeps the register, and it's what most licensed editions do. The duel is what goes missing. When two characters trade chengyu, the reversal only works if the images connect, and two unrelated English idioms don't answer each other.

Paraphrase: drop the idiom and state the meaning. "He was narrow-minded." "They were stunned." This is the fastest and the flattest. A villain who was being sinister in a classical register now sounds like a memo.

What we'd choose

Depends on who's speaking. In narration, paraphrase or equivalent: the narrator's chengyu are shorthand, and the reader should get the meaning without a bump. In dialogue, keep the image when the character is using it on purpose, especially when the idiom is answered, because the wit lives in the picture. And keep it consistent: if the frog in the well appears in chapter five, it should be the same frog in chapter five hundred, not a fence in one place and a well in another. Suppose a sect master tells a young disciple that a frog in a well thinks the sky is a coin, and the disciple, much later and much stronger, tells the sect master's rival that the well was deeper than anyone knew. Replace the frog with a fence and the second line is gone.

How to read it comfortably

Take the four-word saying as a picture. The fable can wait; the image is usually clear in context: a mantis is prey pretending to be a predator, a frog in a well is someone who thinks his well is the world. After a few hundred chapters the common ones become familiar, and you'll start to hear which characters reach for them and which don't, which is its own kind of characterization. We keep each idiom the same picture across a whole book, so the callbacks land; read it in Crossleaf.