Translation:You scratch my back and I'll scratch yours.
There's also the Zen question : "What is the sound of one hand clapping?"
For some reason I'm thinking of the Bap song, sorry about the mistakes, please correct: "Ich geh unheimlich gern mit dir in die WaschSalon, Weil du hast ahnung von der Technik was ich nicht verstonn" (I think verstonn = verstehen in Kölsch).
In my own small world, as a French Canadian, Duolingo's equivalent is faulty... I may be wrong, but I checked my French, my English and my German dictionary, haven't found an answer, but for me, One hand washes the other means some kind of forgiveness... The scratching version means what in French we say "Un service en attire in autre" or help me and I'll help you... Far from my idea of forgiveness...
The meanings seem a little different in English as well.
Duo's translation "...I'll scratch your back" is a kind of a proposition, while "one hand washes the other" is a description of at least two individuals or groups engaging in mutually beneficial activities.
The meanings are similar but the first is someone asking for help and the second is someone describing why or in what way some people are helping each other.
I think, the idiom has a Latin origin (manus manum lavat ) and the original idiom is about corruption. Accompliances will defend each other. "One hand washes the other" seems to be the best choice. Of course there are some idioms about mutuality, which can be acceptable , depending from the context...
In Brazil we have something like "wet someone's hand", meaning to give a tip in advance, so that the person will allow us to do, or will do for us, something that is not correct, for instance, in the restaurant you may "wet the maitre's hand", so that you get a table before other people. It is about corruption!
Native (US) English speaker here: Since these are idioms, I can't be sure of the exact translated meaning. But from the German words, this seems much closer to "One hand washes the other". I guess "You scratch my back and I'll scratch yours" has similar meaning, but all of the words are completely different.
I think hand-washing needs to be made the primary translation, and back-scratching could be an accpeted alternate answer.
Why does it only sometimes accept the literal translation- or rather why would it not teach me the literal translation and then show the English equivalent? This portion is really confusing in that sense. (Ends good all is good- was not an acceptable translation for another sentence.)
"You scratch my back and I'll scratch yours" has negative connotations in English too, again relating to mild corruption, whereas "one good turn deserves another" would generally be thought of as positive. I've never heard anyone say "one hand washes the other" although bribery is sometimes referred to as "greasing someones palm", which will need to be cleaned off afterwards!
So, is the German idiom used with a negative connotation? "One hand washes the other" in English is used to describe a deeper dishonest collusion. It's like a criminal organization exchanging favors for the police in exchange for being allowed to operate their racket. "You scratch my back, I'll scratch yours" often lacks sinister implications. It still may involve some "questionable" practice, but not necessarily.
That's what I thought first, too, as there is a similar idiom in Urdu with negative connotation. But I guess at the bottom of it, it still means that without co-operation, the task can't be done, both positively and negatively. You need one hand to wash another and you need someone WILLING to accept a bribe by the one OFFERING the bribe. Then there is "every drop makes an ocean".
I could be very, very wrong..
In Persian we say nobody can scratch my back, but myself. کس نخارد پشت من. جز ناخن انگشت من گر بخارد پشت من انگشت من. بشکند از بار منت پشت من همتی کو تا نخارم پشت خویش. وارهم از منت انگشت خویش And then the poet say, if my Finger scratch my back then i do Not need anybody in my Life, and because he can Not scratch his back he Said, we must try to Not scratch our back and even i do Not need my Finger to use it for scrathing. And then he Said i am free and needless
We have in Rio de Janeiro, Brazil, a positive way to this proverb: "Gentileza gera gentileza = Kindness produces kindness", it is more than " uma mão lava a outra = one hand washes the other" because in this case, there wasn't interest by the other person in doing a favor.
I can't think of equivalent idiom in Arabic. I don't think that "one hand can't clap" is really similar as we say it when we mean to urge someone to help someone or to accept a help from someone. In this satuation we just say "you help me (with this) and I help you (with that)" or refer to the meaning by any other way.