Ne mogu da slušam muziku glasno, jer to smeta komšinici.

In Serbian, da can have more than one job.

Here it does not mean yes. In ne mogu da slušam, it introduces the second verb and works like to or that in English-style explanations.

So:

• ne mogu da slušam = I can’t listen
• literally, something like I can’t that-I-listen, but in natural English we just say I can’t listen

This is a very common Serbian structure.

Modern Serbian very often uses:

• modal verb + da + present tense

So after mogu, the natural pattern is:

• mogu da slušam
• mogu da radim
• mogu da dođem

An infinitive is possible in some contexts and styles, but in everyday Serbian, da + present is much more common than what an English speaker might expect.

Slušam is the 1st person singular present form of slušati:

• ja slušam = I listen / I am listening

Because it comes after mogu da, Serbian uses the present tense form:

• mogu da slušam = I can listen
• ne mogu da slušam = I can’t listen

So even though English uses to listen, Serbian uses da + present.

Because muziku is the accusative singular form, and it is the direct object of slušam.

• nominative: muzika = music
• accusative: muziku = music as the thing being listened to

With feminine nouns ending in -a, the accusative singular usually changes to -u:

• knjiga → knjigu
• pesma → pesmu
• muzika → muziku

So:

• slušam muziku = I listen to music

Because glasno is an adverb, and it describes how the action is done.

• glasno = loudly
• glasna / glasnu = loud as an adjective

In this sentence:

• slušam muziku glasno = I listen to music loudly

If you wanted to say loud music, then you would use the adjective:

• glasna muzika = loud music
• slušam glasnu muziku = I listen to loud music

So the difference is:

• glasno = loudly
• glasnu muziku = loud music

Yes, but it means something different.

• Ne mogu da slušam muziku glasno = I can’t listen to music loudly
• Ne mogu da slušam glasnu muziku = I can’t listen to loud music

The first focuses on the volume of the action. The second focuses on the type of music.

Jer means because.

So:

• jer to smeta komšinici = because that bothers the neighbor

It is a very common and natural way to introduce a reason.

You can also hear:

• zato što = because

For example:

• Ne mogu da slušam muziku glasno, jer to smeta komšinici.
• Ne mogu da slušam muziku glasno zato što to smeta komšinici.

Both are correct. Jer is shorter and very common in everyday speech.

To refers to the whole idea of listening to music loudly.

So:

• to smeta komšinici = that bothers the neighbor

It does not refer just to muzika by itself. It refers to the situation/action as a whole.

Also, to is grammatically singular neuter, so the verb is:

• to smeta = that bothers

That is why you see smeta, not some plural form.

Because the verb smetati takes the person affected in the dative case, not the accusative.

The pattern is:

• nešto smeta nekome = something bothers someone

So here:

• to = the thing that bothers
• komšinici = the person bothered

That is why it is:

• to smeta komšinici

not:

• to smeta komšinicu

This is an important pattern to learn, because it is different from English grammar.

Komšinici is the dative singular form of komšinica.

Forms:

• nominative: komšinica = female neighbor
• dative: komšinici = to the female neighbor

Since smetati requires the dative, we get:

• smeta komšinici = it bothers the female neighbor

A few related forms:

• komšija = male neighbor
• komšiji = to the male neighbor
• komšinice = vocative, when speaking directly to a female neighbor

So this sentence specifically mentions a female neighbor.

Yes, you could say ne smem, but the meaning changes a little.

• ne mogu da slušam muziku glasno = I can’t listen to music loudly
• ne smem da slušam muziku glasno = I’m not allowed to listen to music loudly

So:

• ne mogu can mean can’t / am unable / it isn’t possible
• ne smem means must not / am not allowed to

In this sentence, ne mogu sounds natural because the reason is practical and social: it would bother the neighbor.

Not completely. Serbian word order is fairly flexible, although some versions sound more natural than others.

The given sentence is very natural:

• Ne mogu da slušam muziku glasno, jer to smeta komšinici.

You may also hear:

• Ne mogu glasno da slušam muziku, jer to smeta komšinici.

That puts a bit more focus on glasno.

Also, the comma before jer is standard:

• ..., jer ...

So the original sentence has both natural word order and correct punctuation.