"Does Corinna buy many foods?"
Translation:Emitne Corinna multos cibos?
Not common, but fine. It probably sounds a bit odd when referring to an individual, because you'd be more likely to enquire whether they buy MUCH food, rather than how many (different types). But if you were talking about a shop, for example, it makes perfect sense to ask whether they buy/sell many foods - i.e. not just quantity, but what range they stock.
I know the word has a plural and it's not wrong strictly speaking, but it just feels off in this context. I'm not a native speaker, but I've been speaking English since I was a kid and I can't imagine asking someone this question. I'd ask about groceries, maaaaybe foodstuffs, but not foods.
I think there's a distinction between something being uncommon, and being wrong. The fact you might not hear or use it very often doesn't make it bad English. And you wouldn't use Latin at all, in everyday life, so there's not really a case that it's "odd Latin", either.
A better translation might be "much food" - which refers to quantity. If you apply the plural form to food it indicates that it is many different types of food. This is somewhat parallel to people and money. If you say peoples you mean several different etnicities or tribes, if you say monies you refer to distinct sums of money.
This is because 'multi cibi' is the nominative form, which would be used if the food was the subject or actor. It is not. In this sentence food is the object and thus must take the accussative form. Here in plural, which makes it cibos. Multos is an adjective that follows the noun that it qualifies - therefore it must also be in accusative.
My understanding (I'm only a learner, like you), is that although Latin word order is generally quite flexible, the verb with the "ne" suffix has to go at the beginning, so the listener gets the heads-up straightaway that what follows is to be construed as a yes/no question.