I do not know Arabic, but there are many things that cannot be exactly translated.
If a story starts with “Once upon a time…” then that phrase in English is telling you something about the nature of the story that follows. That meaning may not be present in the other language.
Translating standard phrases is often difficult. The literal translation of “a red herring” is “a pink fish”, but that is nowhere near the real meaning.
My father once gave a speech, in English, to a Japanese audience while he was in Japan. His speech included a joke, and he got the expected laugh when the translator reached that point. Afterwards, he asked the translator how he had translated the English joke into Japanese. The translator answered, "I said, ‘the professor has just told a joke. Please laugh now.’ " Being Japanese, and very polite, the audience laughed. Was that a good translation of the joke or a bad one?