Learn Hardcore Croatian: Ako mi profesorica sutra vrati zadaću, pregledat ću svaki ispravak što pažljivije. - If the professor returns my homework tomorrow, I will check each correction as carefully as possible.

Breakdown of Ako mi profesorica sutra vrati zadaću, pregledat ću svaki ispravak što pažljivije.

Why is vrati in the present tense if the sentence is about tomorrow?

In Croatian, after ako (if), you normally use the present tense even when the meaning is future.

So:

Ako mi profesorica sutra vrati zadaću...
literally looks like If the teacher returns the homework to me tomorrow...
but in natural English it means If my teacher returns my homework tomorrow...

This is very similar to English in sentences like:

English also uses a present form (comes) after if, even though the situation is in the future.

Also, vratiti is a perfective verb, and perfective present forms often refer to a future completed action in contexts like this.

What does mi mean here?

Mi is the unstressed dative form of ja (I / me), so here it means to me.

Ako mi profesorica vrati zadaću... = If the teacher returns the homework to me...

Croatian often uses a dative pronoun where English might prefer a possessive:

vrati mi zadaću = returns my homework to me / gives my homework back to me

So mi is not the subject. The subject is profesorica.