How long?

yes it looks fine to me.

TeoHow long did you spend studying English last night?

Is the above sentence acceptable?

I don't often disagree with Nona, but the sentence sounds awkward to me. I would change it to: "How long did you study English last night?" or "How much time did you spend studying English last night?"

Teo
How long did you spend studying English last night?

Is the above sentence acceptable?

It's fine, but I think you'll find "much time" with "spend" is more common because of "spend time" and not "use time".

Well, it's true that there are other ways to say it and you may hear contructions like your examples more often, but the original is still grammatical and natural to me. What if "English" were replaced by "for the exam"? Does that sound more natural?

Other examples using the original construction:

Here's a timely one: How long did you spend doing your taxes?

How long did

TeoHow long did you spend studying English last night?

Is the above sentence acceptable?

Interesting Google result:

66,200 - "How much time did you spend".

35,900 - "How long did you spend".