Some well known slang words for “penis” are “Dick” and “Peter” which are common male given names.
Is that phenomena only to English (or other Western European) languages or is it common in Eastern European, Asian and African languages?
Is Schlong a given name?
In Spanish, generally not. However there is a roundabout case. “Pito” (flute or whistle") is a euphemism used for penis, and is also the short form of the name Agapito. In movies with a character named “Dick” where this is used as a double entendre, the Spanish translation will have the character named Agapito in order to make the same pun.
Norwegian has no such slang.
No, it just means “snake” (cf. German Schlange). Probably via Yiddish.
In German, “Willi” (short for Wilhelm) is a not-uncommon moniker for the penis - not as widely-used as “dick”, however. There’s also a saying: “An der Nase eines Mannes / erkennt man seinen Johannes.” (By a man’s nose you know his “John.”)
In Swedish you could say Petter Niklas, it’s quite mild and not particularly common.
Don’t forget Willy and John Thomas. And, if you trust the Pythons, Percy.
Not in Afrikaans - the slang for a penis is piel (pronounced similar to English “peel” but with a shorter vowel)
THE slang? That leads to a follow-up question: do other languages have 3,000 slang words for penis like English does? I had always assumed they did . . .
Is there *any *noun that can’t be used in this way?
Vagina?
Obligatory “Chachi in Korean!” or however that urban legend goes…
Not exactly. It could also be called “pipi”, “voël” (bird) “wors” (sausage) and “pyp” (pipe) or else variants on snake (which, in Afrikaans, is “slang”, ironically enough), but none of those are truly slang the way “piel” is - a rude word in its own right, not just a euphemism. The others would get used in a kind of twee way, but if you want to swear, “piel” is it.
In Finnish, “Jorma” is a very common male name in the age group c. 50 - 80, and also a slang term for penis - so much so, that young people almost snicker when using the name. Maybe as full-size Jormas get rare, the slang term will prevail, as happened with “Yrjö”, a traditional, regal, manly man’s name that in the 1960’s and 1970’s somehow turned into a ubiquituous common language term for “vomit / vomiting” and stayed that way for good.
Here in the States, the only Jorma with whom I’m familiar is Jorma Kaukonen, one-time guitarist for 1960s psychedelic rock band Jefferson Airplane. He is, in fact, in the age group 50-80. 
This is similar to the English usage of “Dick”: Nowadays, most Richards go by Rick or Rich, due to the slang usage, but older Richards grew up in an era before the slang term was widespread, and so “Dick” has remained established for them.
I wonder if that name has anything to do with the sea serpent, Jörmungandr. That would certainly explain why it’s slang for penis.
Hebrew – sometimes uses (used?) what I would translate as “Sammy” (שמוליק) to refer to the penis.
I think it’s dying out though… I’m 50-ish; I not sure my kids would even recognize it. Was never really ubiquitous to begin with, either (plenty of people kept going by “Sammy” in my generation.)
I’m 38, and I’ve never heard that (although I’ve lived a sheltered life). Sure gives that Ariel Zilber song a new meaning.