"What is interesting in this book?"
Translation:מה מעניין בספר הזה?
Ihatethisformatting .מהי is proposed as a translation for "What is". What is this form?
The words מהו/מהי/מהם/מהן are a combination of מה and הוא/היא/הם/הן, and mean "What is/are". As far as I know, they must be followed by a noun:
What is the capital of Israel? = ?מהי עיר הבירה של ישראל (or: מה היא עיר הבירה של ישראל)
What is a table? = ?מהו שולחן (or: מה הוא שולחן)
What is good in the world? = "?מה טוב בעולם"
I think these forms are used less often than what + copula separately ( מהו vs מה הוא ). Is that right? Are they pronounced maí (or ma'í?) / mahú / mahí etc. or differently?
They are pronounced "MAhu", "MAhi", "MAhem", "MAhen".
I think both forms are used a lot in Modern Hebrew, I'm not sure if there's one dominant (also notice that in speech they are said in the same way).
I only know how we speak nowadays, and it's with the stress on the first syllable. Maybe it was supposed to be, originally, with the stress on the last syllable, but I really don't know. :-(