By the time I can handle reading, I've learned enough of the language that I can handle searching for audio-books in my target language.
Basically, you need to know a good translation for "audio-book" in your target language plus the translations of the book titles you're looking for.

If you go to the Wikipedia page for the book you want and change the language (on the bottom left).
So Harry Potter 1 (The Sorcerer's/Philosopher's Stone) is "Harry Potter à l'école des sorciers" (Harry Potter at the school of wizards), and if I were googling sources to purchase, I'd google "Harry Potter à l'école des sorciers livre audio"

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