Chinese. Japanese men just call their dick: chinchin, o chinchin, chinko, o chinko, chinpo or chinpoko... (all variations of the child-like phrase "my peepee" or "my great peepee") you get the idea. The actual word for penis is inkei, but no one in Japan really uses it in conversation, it's something you only see if medical manuals and anatomy books. Chinese is a far more colorful language in general. Japanese doesn't have any where the level of slang and wordplay as English or Chinese, it's a very stodgy and repressed language at its core. Even Japanese cursewords would translate only to mildly rude words in English.
For example, the Japanese insult "kisama" (ki - an honorfic prefix and sama - the well known honorific suffix) was originally a term of honor and respect in addressing members of samurai households who outranked you, used in the same way that just "sama" is used now. But at some point in the Edo period, the word started to drop in social status from indicating a superior to a social equal or an inferior, until in modern day it's become definitely inferior and therefore insulting.
The literal word is still comprised of words that would effectively translate to "Honored Sir" in direct English but because Japan is hyper passive aggressive and snowflakey about their social standings, being called "Honored Sir" in a sarcastic (a concept which exists in Japanese culture only as an insult, it's not funny to them at all) tone is pretty much calling them a son of a bitch or bastard. As a result, Japanese is far more dependent on tone of voice and context for its depth.
Meanwhile Chinese are as vulgar and wacky as Westerners with all their slang and dirty words. We have the same insults you can imagine in English, just in Chinese. You could take the sentence, "You dirty whore, I bet you take dick like a champion you absolute cockgobbler," and have a pretty much word for word equivalent in Chinese. Japanese would translate that into something like, "Oh... you... unaccompanied woman... you like my peepee, yes? I think you do know exactly what you're doing... you lascivious female... please accept this great peepee..." with the last part said in a sarcastic tone to show he's really being alpha.
Side note, this is why I appreciate desioner for translating, because he's familiar with the unspoken contextual meaning of Japanese's very limited dirty vocabulary and he adds the English equivalent flair so it comes across as dirty to us. That is an invaluable skill for subbing dirty talk in JAV, because Japanese are honestly kinda trash at it on the literal level.
The language simply does not live up to the repressed horny demon tentacle monster that hides within every Japanese person.
