Learn Croatian: Dodaj toliko začina u smjesu! - Add that much spice into the mixture!

Toliko translates to "that much" and refers to a quantity near the person you are talking to, or an amount you both just discussed. If the speaker were holding the spoon of spice themselves, they would say ovoliko ("this much"). If they were pointing to an amount further away from both of them, they would use onoliko ("that much over there").

Why is the word for spice (začin) written as začina here?

It is in the genitive case. In Croatian, whenever you use a word of quantity like toliko, ovoliko, malo (a little), or puno (a lot), the noun that follows it must be in the genitive. You can think of it as saying "that amount of spice."

Why is smjesu in the accusative case here instead of the locative?

The preposition u takes the accusative case when there is a clear sense of motion or destination, like adding the spice into the mixture. If you were talking about an ingredient already resting inside the mixture, you would use the locative case (u smjesi).

Why use the perfective verb dodaj here instead of the imperfective form?

Dodaj is the imperative (command) form of the perfective verb dodati. It is used here because the speaker is asking for a single, completed action ("add it in"), rather than telling someone to continuously or repeatedly add spice.