Learn Croatian: Oprosti, nisam oprao posuđe. - Sorry, I didn't wash the dishes.

The speaker is apologizing for not finishing a specific task. The perfective verb oprati focuses on the successful completion of an action. By saying nisam oprao, they mean "I didn't get the washing done." If they used the imperfective nisam prao, it would mean "I wasn't washing" or "I didn't spend any time washing," which sounds unnatural here because the focus is on the uncompleted result, not the process.

How do we know the speaker of this sentence is male?

We can tell by the ending of the past tense verb oprao. The -o ending is used for masculine singular subjects in the past tense. If a woman were speaking, she would use the feminine ending and say nisam oprala.

The English translation says "dishes" (plural), but posuđe doesn't look like a plural word. Why is that?

posuđe is a collective noun. This means it refers to a group of items as one single mass concept, much like the English words "cookware" or "tableware". Grammatically, it behaves exactly like a singular neuter noun. Here, it is in the accusative case because it is the direct object receiving the action of the verb.

Is the word oprosti (sorry) related to verbal aspect too?

Yes! Oprosti is the informal command form of the perfective verb oprostiti (to forgive). We use the perfective aspect here because you are asking someone to forgive you for this one specific thing that just happened, rather than asking them to be in a continuous state of forgiving you over time.