"What does their dinner include?"
Translation:Τι συμπεριλαμβάνουν στο δείπνο τους;
Oh, sorry (was quite surprised because your posts are always so exact) it was my misunderstanding. The plural συμπεριλαβάνουν" refers to the items (dishes) that are included in the meal. E.g. "What things does their meal include." Which is why I said the "nouns" because I thought of "salad" "potatoes" "wine" ... Hope that helps.
It would also be possible to use "συμπεριλαμβάνει" in a general sense.
Hope that helps.
Of course, the plural is for "they" now it all makes sense. thank you. So the translation should be: "What do they include in their dinner?" I'm changing it now. Thank you ShaoxuanLi for realizing there was something wrong with the translation and thank you mizinamo for finding the solution.