The expression “it takes two to tango” means that two people are needed for certain activities, or that both people involved in a particular activity or situation share equal responsiblity for it.
It apparently comes from the 1952 song Takes Two to Tango by Al Hoffman and Dick Manning [source].
In Russian an equivalent idiom is один в поле не воин (odin v pole ne boin), or “one in the field is not a warrior”. Perhaps this comes from the idea that a warrior with nobody to fight againt on a battle field is not really a warrior. Does anybody know the origins of this phrase?
This idiom is also translated as “one man is an island”, “safety in numbers”, “you don’t have to do this alone” or “you never get far on your own”. Some examples of how it’s used include:
Один в поле не воин, как бы кому-то этого не хотелось.
No man is an island however much they want to be.
Мне они тоже не нравятся, но один в поле не воин.
I don’t like them either, but this war is bigger than us.
Но ты же прекрасно понимаешь, что один в поле не воин.
But right about now, my army-of-one situation is not cutting it.
Source: Reverso.
Are there interesting equivalent idioms in other languages?
Dahl gives “один в поле не воин” together with “одной рукой и узла не завяжешь” (one cannot tie a knot with one hand), and there’s another proverb “один солдат — не полк” (one soldier isn’t a regiment), so a more likely interpretation is that one warrior by himself won’t win a battle.