W refrenie śpiewamy razem głośniej niż w zwrotce.

Because the preposition w often means in and requires the locative case when it answers the question where?

So:

• refren → w refrenie = in the chorus
• zwrotka → w zwrotce = in the verse

This is a very common pattern in Polish:

• w domu = in the house
• w szkole = at school
• w piosence = in the song

So here both nouns are in the locative because we are talking about where the singing happens.

Refren means chorus or refrain in a song.

It is the part that repeats, usually after each verse. In music vocabulary:

• refren = chorus / refrain
• zwrotka = verse

So the sentence contrasts two parts of a song: the chorus and the verse.

Zwrotka means verse in a song or poem.

In this sentence, w zwrotce means in the verse. It is being compared with w refrenie:

• W refrenie = in the chorus
• w zwrotce = in the verse

Śpiewamy is the 1st person plural form of śpiewać = to sing.

It can mean:

• we sing
• we are singing

Polish present tense often covers both the simple present and the present continuous, depending on context.

Here it most naturally means something like:

• we sing together louder in the chorus than in the verse
• or in the chorus, we sing together more loudly than in the verse

It can sound like a general statement about how the song is performed.

Because Polish usually does not need subject pronouns when the verb ending already shows who is doing the action.

• śpiewam = I sing
• śpiewasz = you sing
• śpiewamy = we sing

So śpiewamy already contains the idea of we. You could add my for emphasis, but it is not necessary:

• My śpiewamy razem... = We sing together...

That would sound more emphatic, not neutral.

Razem means together.

So śpiewamy razem means we sing together.

It tells us how the action is done: not separately, but collectively.

You can use razem in many everyday contexts:

• Idziemy razem. = We are going together.
• Mieszkamy razem. = We live together.
• Zróbmy to razem. = Let’s do it together.

Because głośniej is the comparative form of głośno.

• głośno = loudly
• głośniej = more loudly / louder

The sentence is making a comparison:

• głośniej niż... = more loudly than...

So:

• Śpiewamy głośno. = We sing loudly.
• Śpiewamy głośniej niż wcześniej. = We sing more loudly than before.

Here, the comparison is between singing in the chorus and singing in the verse.

Niż means than in comparisons.

The pattern is:

• comparative form + niż
  • the thing being compared

So here:

• głośniej niż w zwrotce = more loudly than in the verse

Other examples:

• szybciej niż ja = faster than me
• lepiej niż wcześniej = better than before
• więcej niż rok = more than a year

So głośniej niż w zwrotce is a standard Polish comparison.

Because each phrase needs its own preposition.

You are comparing two locations or contexts:

• w refrenie = in the chorus
• w zwrotce = in the verse

Polish keeps the preposition with both parts. In English, we might sometimes shorten this kind of structure, but in Polish repeating w is normal and natural.

No, Polish word order is fairly flexible, though some orders sound more natural than others depending on emphasis.

The original sentence:

• W refrenie śpiewamy razem głośniej niż w zwrotce.

This is natural and puts focus first on where: in the chorus.

You could also say:

• Śpiewamy razem głośniej w refrenie niż w zwrotce.

This is also understandable, but the emphasis shifts a little.

Polish often moves elements around for focus, topic, or style. The original version sounds very natural if you want to contrast the chorus with the verse right away.

A few helpful pronunciation notes:

• refrenie: roughly ref-RE-nye
• śpiewamy: roughly shpye-VA-mih
• głośniej: roughly GWO-shnyey

Useful details:

• ś is a soft sh sound
• ie after some consonants often softens them
• ł sounds like English w
• ń is a soft ny sound
• j sounds like English y

So głośniej has:

• gło ≈ gwo
• śń ≈ a soft shn
• ej ≈ ey

Here it is an adverb, because it describes how we sing.

It comes from:

• adjective: głośny = loud
• adverb: głośno = loudly
• comparative adverb: głośniej = more loudly

Since it modifies the verb śpiewamy (we sing), the adverb is needed.

Compare:

• To jest głośna piosenka. = This is a loud song.

  • głośna = adjective

• Śpiewamy głośno. = We sing loudly.

  • głośno = adverb

Yes, that is also a reasonable English translation.

Because razem can be understood as together, its exact position in English can vary a little:

• In the chorus, we sing together louder than in the verse.
• In the chorus, we sing louder together than in the verse.
• In the chorus, we all sing louder than in the verse.

The Polish sentence itself clearly means that we sing together, and that this singing is louder in the chorus than in the verse. English can phrase that a few slightly different ways.