Kiedy nikt nie narzeka i niczego nie brakuje, wieczór z dobrą komedią naprawdę się udaje.

Because Polish uses negative concord. If you have a negative pronoun like nikt (nobody) or nic / niczego (nothing), the verb is normally negated too.

So:

• nikt nie narzeka
• niczego nie brakuje

This is standard, correct Polish. Unlike in English, it is not considered a mistake or an illogical “double negative.”

Niczego is the genitive form of nic.

The verb brakować usually takes the thing that is missing in the genitive:

• brakuje czasu = time is lacking
• brakuje pieniędzy = money is lacking
• niczego nie brakuje = nothing is lacking

So niczego is used because it matches the case required by brakować.

You may sometimes hear nic nie brakuje in everyday speech, but niczego nie brakuje fits the standard pattern very neatly.

The verb brakować means to be lacking, to be missing, or to be absent.

It works differently from English. Polish often says something closer to:

• brakuje czegoś = there is a lack of something / something is missing

So niczego nie brakuje is literally something like:

• nothing is missing
• there is no lack of anything

It is not built like English someone lacks something quite as directly, even though that meaning can overlap.

Yes, but the nuance changes.

• kiedy = when / whenever
• jeśli / jeżeli = if

In this sentence, kiedy suggests a general situation or recurring pattern: whenever those conditions are true, the evening goes well.

If you used jeśli, it would sound more like a condition:

• Jeśli nikt nie narzeka... = If nobody complains...

So kiedy feels more natural here for a general truth.

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

Structure:

• Kiedy nikt nie narzeka i niczego nie brakuje, = subordinate clause
• wieczór z dobrą komedią naprawdę się udaje. = main clause

In Polish, clauses like this are normally separated by a comma.

Because wieczór here is a noun meaning an evening, and it is the main thing being talked about.

• wieczór = an evening
• wieczorem = in the evening

So:

• Wieczór z dobrą komedią się udaje = An evening with a good comedy turns out well
• Wieczorem... would mean In the evening..., which is a different idea

Because z meaning with takes the instrumental case.

Base form:

• dobra komedia

After z:

• z dobrą komedią

Both words change because the adjective must agree with the noun:

• dobra → dobrą
• komedia → komedią

A useful contrast:

• z dobrą komedią = with a good comedy → instrumental
• z domu = from the house → genitive

So z can take different cases depending on its meaning.

Here udaje się is part of the fixed verb expression udawać się / udać się, which means:

• to succeed
• to turn out well
• to go well

So wieczór ... się udaje means that the evening works out well or is a success.

The się here is not something you should translate literally as itself. It is just part of how this verb is used.

Because udaje się fits a general, habitual meaning.

This sentence is describing what typically happens under certain conditions, so Polish uses the imperfective idea:

• udaje się = goes well / tends to go well

If you were talking about one specific future evening, you would more likely use:

• uda się = will turn out well

For example:

• Jeśli nikt nie będzie narzekał, wieczór się uda. = If nobody complains, the evening will turn out well.

Because brakować is very often used in an impersonal 3rd-person singular pattern.

In niczego nie brakuje, the missing thing is not treated as a normal nominative subject. Instead, it appears in the genitive (niczego), and the verb stays in singular:

• brakuje czasu
• brakuje pieniędzy
• niczego nie brakuje

This is a very common Polish structure.

Yes, Polish word order is fairly flexible, but this version is neutral and natural.

The sentence first gives the circumstance:

• Kiedy nikt nie narzeka i niczego nie brakuje,

and then the result:

• wieczór z dobrą komedią naprawdę się udaje.

You could move some parts around for emphasis, especially naprawdę, but the given order sounds smooth and unmarked.

Naprawdę means really, truly, or genuinely.

It adds emphasis:

• not just that the evening is okay,
• but that it really turns out well.

If you remove naprawdę, the sentence is still grammatical, but a little less expressive.