Batman is apparently heavily inspired by the philosophy of Nietzche. The quote is probably a more polished version of this one from Beyond Good and Evil: "He who fights monsters should see to it that he himself does not become a monster. And if you gaze for long into an abyss, the abyss gazes also into you."

So maybe somewhat German after all.

Source: https://movies.stackexchange.com/questions/10572/is-this-quo...