Neither do I and I'm also french. I've checked on the french wiktionary[1] and in fact that's a real french saying. But I've never heard someone say this in my all life.
Seems to be a mix betwen of "Je m'en bats les couilles" and "Le train de tes injures roule sur les rails de mon indifférence", never heard the author version. I stand wrong on the etymology, see below. French-speaking here.
It exists as an entry in the https://fr.m.wiktionary.org/wiki/s%E2%80%99en_badigeonner_le... but I don't think I ever heard someone uses it. The non vulgar original version seems to be "s'en brosser le nombril avec le pinceau de l'indifférence" (To brush one navel with the brush of indifference) and found it's origin in the comic strip Achille Talon.
There are just a lot of different ways to say it, and although this one isn't very popular most people would still get the meaning fine and it does have some attested use, so I think it has its place in such a list.
My own personal favorite would be (it's very inelegantly translated) it touches one [of my testicles] without making the other move (maybe invented by former president Chirac, at least made popular by him). It's well known and understood and has the advantage to be vulgar enough without actually making an explicit reference to testicles.
I'm French from Québec and the usual expression here would be the Catholic inspired "I'm X-ing myself of it" where X is one of Christ (je m'en crisse), the Holy Chalice (je m'en câlice), the Tabernacle (je m'en tabarnac) etc.
Although these swears seem extremely mild, they are actually quite heavy in Québec, even though no one goes to church anymore, because of how dominant the Catholic Church was until the sixties. They would be censored on TV, for example.
French speaking, never heard of this one. For the sake of human advancement, I'll share with you the one that I hear more often "je m'en bats les coui*es" (literally "I hit my ba*s with it" or something like that; which means "I don't care).
That happens when you google idioms in other languages ... you have no clue about the actual usage. And they are usually not one-to-one.
German "das ist mir Wurst" is also a lot weaker than "zero fucks given", at least use something stronger like "das interessiert keinen Arsch" (no asshole cares). Also "zero fucks given" in the sense of "irresponsible, he just does it and doesn't care who gets hurt" doesn't really have an equivalent idiom. Maybe "als druff" (just go full power straight ahead) or something.
I've never heard "als druff" but I'd like to add "das ist mir Latte" as a variant as well as "das ist Jacke wie Hose" ("jacket like trousers", which is more like "potayto, potuhto") and as others have pointed out "das geht mir am Arsch vorbei".
But none of them is an exact match as there's no perfect overlap for all situations to which "zero fucks given" can be applied. Which isn't too surprising as most idioms and even most words don't map 1-to-1 between languages even when they share a common root.
Yeah, "das ist mir Wurst" doesn't seem strong enough. "Drauf geschissen"/"Scheiß drauf" ("shit on it") maybe? Kinda close to "not giving a shit" (or "fuck") and also kinda works for the irresponsible case, "Er scheißt drauf, ob er jemanden verletzt".
That sounds beautifully poetic, compared to versions from other languages (mine included). I can see how Monty Python came up with "I fart in your general direction" :)
"Je m'en fous" is the short version. Using a longer version is obviously done for fun, and to tell at great lengths how much you don't care. Usually people will spice it up with a version of their own to add to the comical effect.
Why talk when you can physically convey the idea. I must say that this discussion makes me somewhat uncomfortable with the centrality of not caring in my culture.
If anyone has an idea of the original in french, I would be interested. I am French and I have no clue what he refers to.