This was a really satisfying sentence to translate. The longer answer made for a more interesting exercise, not necessarily because of having more context but also because of simply having more to translate!
One dictionary I consulted gives both teacher and professor for athro, but DL marks 'professor' wrong.
Has the teacher a dictionary. Yes he has a good one. should be equally acceptable.
"Has he an x" is not idiomatic English.
Would this also be acceptable ?A yw'r athro wedi cael geiriadur