Is "How is the bank?" correct English?
It sounds to me more like you're asking how the bank itself is doing :)
Yes, it means the same thing as "What is the bank like?" to me, at least if you're asking someone about their experiences with the bank.
Yes, that would be pretty normal colloquial English. Though depending on context it could be asking either about the status of the bank or about the experience of going to the bank.
A translation option for milyen is 'what kind of', but 'what kind of bank is this?' was not accepted. Don't understand why.
"What kind of bank is this?" translated is "Milyen bank ez?"
Why is the translation "How is the bank?" not accepted?
Because it is not how you would say it in English.
"What kind of bank is it?" Not accepted, so, fair enough. But how WOULD you say "What kind of bank is it?" in Hungarian?
"What kind of bank is it?" - Milyen bank ez? /Milyen bank az?