In Mandarin, “*guei-tou *(turtle-head)” is slang for the penile glans while “xiao niao (little bird)” is slang for the penis itself as a whole.
Let’s not forget the not-quite-German Schwanzstucker…
“Dole” is NOT the slang term for “penis” in Farsi, which caused some uncomfortable moments on Iranian TV during the 1996 U.S. presidential campaign.
Realizing this post is 16+ years old, I still must respond: I don’t think “chin-chin” (usually o-chin-chin) is particularly slangy; in any case, it’s not a rude word because you can hear it on non-comedy Japanese TV shows from time to time. For really serious discussion they use the transliterated English word “penis” but most of the time “o-chin-chin” is perfectly fine.
My Japanese husband says that the only rude word he knows is “chin-bo-ko.”
Is it enormous? 
*
Oh, sweet mystery of life at last Ive found you!
Oh, at last I know the secret of it all.
*
I was going to post this. Our children were born in Japan and when they’re talking about little boys penises, they always say “o-chin-chin“.
The normal slang term is the Japanese word for “that“ which is “are.” (“a” as in “father” and the “e” as in “bed.”)
It’s not a dirty word, though.
Dutch: Pik, piemel, lul, lummel, leuter, snickel, jongeheer. For starters. And welcome to our new member dopiest, who joined solely to resurrect this thread, it would seem. Kicking it old-school sdmb from day one.
Japanese
chin- with various endings and prefixes — a few others have provided examples. This makes teaching detailed facial anatomy to children inadvisable. (Teacher: “This is my chin!” Boys: <pointing to crotches> “This is my chin!”) For similar reasons, teaching extended family words is potentially hazardous to classroom decorum. (Uncle sounds like unko <うんこ; feces/poo/shit>).
Chin-chin (ちんちん) is analogous to kids saying “pee-pee” in English, as in “My pee-pee hurts.”
Chin-ko (ちんこ); chin-po (チンポ) are regional variations on pronunciation — the connotation is similar to “cock” in English. Katakana works a lot like italics or bold type in English does for emphasis, so katakana versions in writing “feel” stronger/nastier.
デカチン deka-chin — big cock.
related: チンピラ chinpira — punk, little shit, low-level gangster
Katakana-English ペニス penisu is sometimes used for “flavor”; depending on the situation it can make it feel either more clinical or more raunchy. コック kokku on the other hand, as a transliteration of “cock” is always dirty.
棹 さお sao — rod ･ pole ･
太マラ futomara — fat cock, thick one, choad.
息子、息 むすこ musuko (lit. “son”) euphemism, like saying “little <insert user name here>“, or mini-me.
男根 だんこん dankon — lit. “man root”
陽根 ようこん: youkon — 陰 in and 陽 you are the Japanese versions of Chinese yin (female) and yang (male) spirit/force/influence, so this could be translated fairly literally as “the root of maleness”. 陽物 ようぶつ youbutsu — lit. “male thing”
カリ首、雁首、鴈首 <カリくび karikubi> — lit. “goose neck” glans, penis
尺八を吹く、〜する しゃくはち shakuhachi o fuku — lit. playing the Japanese end-blown flute; sucking cock, giving a blowjob
Spanish
la verga — (vulgar) cock, prick
el pene — penis
Brazilian Portugese
piroca (unsure of spelling, article) Learned from Brazilian friend. Definitely crude, probably a male-only word.
pene is not slang, it’s the official name. The non-slang meaning of verga is horsewhip.
Not penis as such, but capullo (officially, flower bud) is a slang name for the dick’s head. So, when capullo is used as an insult it is directly equivalent to the English word “dickhead” both in meaning and imagery.
I enjoyed this so much, I must contribute. I had a Moldovan girlfriend, but in the early years, the only language we shared in common was Russian. She used the term ‘kotYONochek’ котёночек, which I would translate as tomcat. It is more an intimate term rather than offensively vulgar.
Perereca (tree frog) is the vulgar term that essentially means pussy.