"Quels sont tes livres préférés ?"
Translation:What are your favorite books?
From what I learned the word "quels" translates to "which", and I know in English using "what" is accepted as well. Does this mean that in French, I can use "Quels" as "what" in any place where the words "which" and "what" are interchangeable in English? thanks a lot!
"Quel" may mean either "which" or "what". The former is used in the sense of selection from some available choices. "What" is used is the sense of an open-ended question.
There is a monthly magazine in the UK called What Car? that is aimed primarily at car buyers rather than ardent enthusiasts. It compares and contrasts models new and old. Every time I see a new edition on a newsstand I shout (internally, you understand) WHICH Car?! Because, as you rightly point out, it is asking me to select from among available choices. We also have What Hi-Fi? and What satellite?. Fortunately, this is all counterbalanced by a consumer magazine that examines a wide range of goods and services, called simply: Which?
Préférer is a stronger word in French than preferences. It means "favorite". Alternatively you can possibly say "what are your preferred books?" but that still isn't quite the same meaning.
Shouldn't this sentence translate to "what are your preferred books?" since préférés is literally "preferred" and adjectives with literal (instead of figurative) meanings are put postnominally?
"What are your favourite books" to me implies what sort(s) of books? If I wanted to ask about which specific books someone likes, would I say "Lesquels sont tes livres préferés?"
"Which books are your favorites" is wrong why? Plural books means there must be more than one favorite, no? Unless one is asking about a genre of books; in which case, how would one know that? Seems to me the question is asking for a list of favorite books.
You may feel free to rephrase the English sentence when the more direct translation does not produce an idiomatic (natural) expression. Here, the translation of "what/which are your favorite books?" is completely natural. There is no reason to rewrite it into another form. In your sentence, "favorites" is a noun. In the French sentence, "préféres" is an adjective. So unless it is just terribly awkward English, stay with the same general structure. This is the approach used throughout Duolingo.
That is not in the database of translations. If this happens again, can you please get a screenshot?