Learn Croatian: Dodaj peršin i lovor u juhu. - Add parsley and bay leaf to the soup.

In recipes and instructions, Croatian usually uses perfective verbs for single, completed actions. You add the ingredients once and move on. You would use the imperfective dodavaj only if you were told to add them continuously or repeatedly over a period of time.

Why does the sentence use u juhu (accusative) instead of u juhi (locative)?

The preposition u takes the accusative case when there is a sense of motion or direction towards a destination, like putting something into the soup. If you were describing ingredients that are already resting inside the soup, you would use the locative case (u juhi).

Since peršin and lovor are direct objects, why don't their endings change for the accusative case?

They are actually in the accusative case! Because they are inanimate (non-living) masculine nouns, their accusative form is identical to their dictionary (nominative) form. If you were adding an animate masculine noun, the ending would change, for example, dodaj raka (add a crab).

Does lovor specifically mean 'bay leaf' or the laurel plant in general?

Lovor refers to the laurel tree or shrub itself, but in a culinary context, it is widely used as a shorthand for the spice. You will also frequently hear the full phrase lovorov list (laurel's leaf) used in recipes.