I was thinking in the instance of nominative vs accusative. But if you want to speak broadly, if you would say Он in Russian, say he. If you would say его, ему, им, or нем, say him. Likewise with она and she. Also if you would say Кто, say who. If you would say кого, кому, кем, or ком, say whom.
I can't think of any exceptions to this. Maybe you can help think something up.![]()