Kiedy rozpakuję ostatni karton i skończy się remont, wreszcie zrobi się porządek w przedpokoju.

Rozpakuję is the perfective non-past form of rozpakować. In Polish, perfective verbs do not normally describe a present action; their non-past forms usually refer to the future.

So:

• rozpakowuję = I am unpacking / I unpack (imperfective, present)
• rozpakuję = I will unpack (perfective, future)

Here the speaker means a completed future action: once the last box has been unpacked.

Because the sentence focuses on the action being finished, not on it being in progress.

Compare:

• Kiedy rozpakuję ostatni karton... = When I unpack / have unpacked the last box...
• Kiedy będę rozpakowywać ostatni karton... = When I am unpacking the last box...

The first version fits better because the next event happens after the unpacking is completed. Perfective verbs are very common in Polish for this kind of meaning.

That is a very common difference between English and Polish.

In Polish, if the whole situation is in the future, the verb in a kiedy clause is often also in a future form:

• Kiedy rozpakuję...
• Kiedy skończy się remont...

English usually avoids will after when, but Polish does not work the same way. So this is normal and natural Polish.

It is in the accusative, because it is the direct object of rozpakuję.

The verb rozpakować takes an object:

• rozpakować karton = to unpack a box

Here:

• ostatni = last
• karton = box / carton

For a masculine inanimate noun like karton, the accusative singular looks the same as the nominative singular. So even though it looks unchanged, it is still functioning as the accusative.

This means something like the renovation will end / come to an end.

The subject is remont, so grammatically:

• remont = subject, nominative
• skończy się = will finish / will end

Polish often uses skończyć się for events, processes, seasons, meetings, renovations, etc.:

• Film się skończył = The film ended
• Remont się skończy = The renovation will end

So skończy się remont is a very natural way to say the renovation will be over.

In this sentence, się is not a separate word with a simple one-word translation like self. It is part of the verb construction.

Two slightly different ideas are involved:

• skończyć się = to end / to come to an end
• zrobić się = to become / to get

So:

• skończy się remont = the renovation will end
• zrobi się porządek = order will be established / it will become tidy

For learners, it is best to treat skończyć się and zrobić się as whole verb expressions.

Both are possible in some contexts, but they are not exactly the same.

• będzie porządek = there will be order
• zrobi się porządek = order will get made / things will become orderly

Zrobi się emphasizes a change of state: now things are messy, but later they will become orderly.

So in this sentence, zrobi się porządek sounds more dynamic and natural because the speaker is talking about the moment when the chaos finally turns into order.

Yes, grammatically porządek is the subject.

In zrobi się porządek, Polish uses a kind of impersonal/resultative construction, but porządek is still in the nominative, not the accusative.

That can feel unusual to an English speaker, because English might prefer something like:

• there will finally be order
• the hallway will finally be tidy

But in Polish, porządek is the thing that comes about.

Because w meaning in takes the locative case when it refers to location.

The base form is:

• przedpokój = hallway / entrance hall

In the locative singular, it becomes:

• w przedpokoju = in the hallway

So this is a standard preposition + case pattern:

• w domu = in the house
• w pokoju = in the room
• w przedpokoju = in the hallway

Yes. Polish word order is fairly flexible, though some orders sound more natural than others depending on emphasis.

For example, these are possible:

• Kiedy rozpakuję ostatni karton i skończy się remont, wreszcie zrobi się porządek w przedpokoju.
• Kiedy rozpakuję ostatni karton i remont się skończy, wreszcie zrobi się porządek w przedpokoju.
• W przedpokoju wreszcie zrobi się porządek, kiedy rozpakuję ostatni karton i skończy się remont.

The original sounds natural and well-balanced. It presents the two conditions first, then the final result.

Wreszcie means finally / at last. Its position helps highlight the speaker’s feeling of relief.

In the original sentence:

• ..., wreszcie zrobi się porządek w przedpokoju.

This placement makes wreszcie modify the whole result clause: finally, the hallway will become orderly.

You could move it, but the emphasis changes slightly:

• Wreszcie zrobi się porządek w przedpokoju = strong emphasis on finally
• Zrobi się wreszcie porządek w przedpokoju = also possible, slightly different rhythm

Because the sentence begins with a subordinate clause introduced by kiedy:

• Kiedy rozpakuję ostatni karton i skończy się remont = subordinate time clause
• wreszcie zrobi się porządek w przedpokoju = main clause

In Polish, when a subordinate clause comes before the main clause, you normally separate them with a comma.

Yes. The sentence presents two linked future conditions/events:

• I unpack the last box
• the renovation ends

Only then does the result happen:

• there will finally be order in the hallway

So the structure implies that both things are part of what needs to be completed before the final situation is achieved.

Usually kiedy is the safer and more standard choice here.

• kiedy = when
• jak can sometimes mean when, but it is more colloquial and can also mean how

So for a learner, kiedy is the best option in this sentence:

• Kiedy rozpakuję ostatni karton... = clear, standard Polish

Here remont refers to the whole renovation as a single process or project.

So:

• skończy się remont = the renovation will end / be over

Even though remont is grammatically a countable noun, in this sentence it behaves like the name of an ongoing process or event, similar to English the renovation or the remodeling.

It breaks down like this:

• Kiedy rozpakuję ostatni karton = when I unpack the last box
• i skończy się remont = and the renovation ends
• wreszcie zrobi się porządek = finally order will be established / things will finally become tidy
• w przedpokoju = in the hallway

So the pattern is:

When X and Y happen, Z will finally happen.

That is a very common and useful Polish sentence pattern.