Of course it is common in China, It is a word in their language. I never said it isn't, i mean translate it literary word by word to TO ENGLISH, as black"belly" ain't work. Just like in English when one say "heart" they ain't mean the internal orgasm one.
still better than translate to a words and loss 100% it meaning.
Yeah, "Nakama mean...", words sometime have more specific description that don't have the 100% equivalent word in another language, But translate it to belly don't even work to transfer even half of it then what is the point ? Belly in English ain't use the same way Asian language use it, but "Heart" is a closest equivalent.
and if you translate it to belly, then with a note anyways, then want to provide the extra sense ? why can't do the same with heart
Do you keep this same energy for terms of address like jiejie and xuejie? Or, assuming you read manga, onee-san and senpai? I imagine you, like many Westerners, prefer those (especially familial) terms untranslated, because calling your romantic partner Sister (or even sis) is probably jarring compared to the built-in "not always referring to family" understanding with jiejie/name-jie
Do you make the same complaints when two faced women are called "green teas" or "white lotuses"? Because you know no English speaking country is going to assume the meaning without an explanation, and even with an explanation it doesn't "track" with western cultural knowledge.
Genuinely not trying to argue, just trying to help you understand the purpose in keeping specific cultural terms versus taking liberties/localization with the translation.
Like in this example we're literally talking about two different accusations: if you call someone black hearted and all they do on the surface is act chivalrous you'll sound crazy - but to call them black bellied is a warning that under their charming surface they are a wicked soul. It's like the difference between calling someone two faced and calling them an evil bastard
Sorry for the rant, mostly leaving this here in case others are curious about the topic, but long story short, localized translation can easily cheat the reader out of a full and comprehensive reading experience