"Yönetmen onun babasıdır."
Translation:His father is the director.
Where in this sentence is the accusative found to make it "the director" and not "his father is a director"
His father is a director → Onun babası yönetmen(dir).
The current Turkish sentence is: "Yönetmen onun babasıdır." ("Director", that would be his father.) Placing it at the beginning sort of stresses it. Paraphrasing is one of our little tricks to circumvent the problem of "absence of a linguistic 'the'". Perhaps in 200 years, Turkish will develop a "the", but for now, we should make do with paraphrasing. :)