Learn Hardcore Polish: Wieczorem trudno mi zasypiać, gdy sąsiedzi oglądają głośny film. - In the evening it is hard for me to fall asleep when the neighbors are watching a loud movie.

You can say wieczorem or wieczorami (in the evenings, regularly).
W wieczór is not idiomatic in modern Polish; you might see tego wieczoru (that evening) instead when you mean a specific evening.

What exactly does trudno mi zasypiać mean literally? Why no subject like ja?

Literally, trudno mi zasypiać is:

trudno – it is difficult
mi – to me / for me (dative of ja)
zasypiać – to fall asleep (imperfective, infinitive)

So the structure is impersonal:

(Jest) trudno mi zasypiać – (It is) difficult for me to fall asleep.

Polish often uses such impersonal expressions with adjectives/adverbs + dative:

łatwo mi to powiedzieć – it’s easy for me to say that
ciężko nam pracować w nocy – it’s hard for us to work at night

There is no explicit subject (no ja) because the “subject” is really the action zasypiać (to fall asleep), and the person affected is expressed with dative (mi).

Why is it mi, not mnie, in trudno mi zasypiać?

Both mi and mnie are dative forms of ja (I), but:

mi is the unstressed / clitic form
mnie is the stressed / full form

In neutral sentences, the short form usually comes after the verb or predicate word:

trudno mi zasypiać – it’s hard for me to fall asleep
jest mi zimno – I am cold (literally: it is cold to me)

You use mnie when you want to put extra emphasis on the person:

Mnie jest trudno zasypiać, a nie jemu.
It’s ME who has trouble falling asleep, not him.

So trudno mi zasypiać is the normal, unstressed version.

Why is it zasypiać and not zasnąć? What’s the difference?

Both relate to falling asleep, but they differ in aspect:

zasypiać – imperfective: the process / repeated action
zasnąć – perfective: a single completed event (the moment you finally fall asleep)

In this sentence, we’re talking about a repeated difficulty, a general habit:

Wieczorem trudno mi zasypiać – In the evenings it’s hard for me to (manage to) fall asleep.
→ Describes an ongoing, habitual problem.

If you said:

Wieczorem trudno mi zasnąć

you’d usually mean “On a given evening, it’s hard for me to actually fall asleep (reach that point).” It focuses more on reaching the end point once, not on a habitual situation.

Why is the infinitive zasypiać used after trudno? Is there a pattern?

Yes. Polish often uses the structure:

(jest) + adjective/adverb + (komuś – dative) + infinitive

Some common patterns:

trudno mi zasypiać – it’s hard for me to fall asleep
łatwo ci to powiedzieć – it’s easy for you to say that
miło nam pana poznać – (it’s) nice for us to meet you
nudno mu tam siedzieć – (it’s) boring for him to sit there

The infinitive expresses the action, and the dative (mi, ci, nam, etc.) is who finds it easy/hard/boring/etc.

Could I say Wieczorem jest mi trudno zasypiać instead? Is that wrong?

It’s not wrong; it’s grammatical and understandable:

Wieczorem jest mi trudno zasypiać.

However, in everyday speech the “jest” is often dropped, and trudno is placed first:

Wieczorem trudno mi zasypiać. (more natural, smoother)

Adding jest makes the sentence a bit more explicit and sometimes slightly more formal or heavy, but it’s okay. The meaning is essentially the same.

What’s the difference between gdy and kiedy here? Could I use kiedy instead?

In this context, gdy and kiedy are practically synonymous:

…gdy sąsiedzi oglądają głośny film.
…kiedy sąsiedzi oglądają głośny film.

Both mean when (introducing a time clause). Nuances:

gdy is often slightly more formal / literary.
kiedy is more neutral / conversational and also used in questions:
Kiedy wrócisz? – When will you come back?

So yes, you can replace gdy with kiedy here without changing the meaning.

Why is there a comma before gdy?

In Polish, a comma normally separates a main clause from a subordinate clause introduced by conjunctions like:

gdy, kiedy, ponieważ, że, jeśli, chociaż, etc.

Here:

Main clause: Wieczorem trudno mi zasypiać
Subordinate time clause: gdy sąsiedzi oglądają głośny film

So you must write:

Wieczorem trudno mi zasypiać, gdy sąsiedzi oglądają głośny film.

You could also reverse the order:

Gdy sąsiedzi oglądają głośny film, wieczorem trudno mi zasypiać.

and you still need the comma.

Why is sąsiedzi in the nominative plural, not some other case?

In the clause gdy sąsiedzi oglądają głośny film, the subject of the verb oglądają is sąsiedzi:

kto? co? ogląda? – sąsiedzi (who is watching? – the neighbors)

Subjects in Polish take the nominative case, here plural masculine personal:

singular: sąsiad (neighbor – male)
plural: sąsiedzi (neighbors – at least one male in the group)

So sąsiedzi must be nominative because it is the grammatical subject of oglądają.

Why is the verb oglądają and not something like patrzą film or oglądają na film?

Polish verbs for “look/watch/see” work differently from English:

oglądać coś – to watch something (TV, a movie, a show, etc.)
→ takes a direct object in the accusative
- oglądać film, oglądać serial, oglądać mecz
patrzeć (na coś) – to look (at something)
→ requires the preposition na
- accusative
- patrzeć na ekran, patrzeć na telewizor
widzieć coś – to see something (the state of seeing, not intentional watching)

So for “watching a movie” the natural verb is oglądać:

sąsiedzi oglądają film – the neighbors are watching a film

Patrzą film and oglądają na film are both incorrect.

Why is it głośny film and not something like film głośny? How does word order work with adjectives?

In Polish, attributive adjectives (those that directly modify a noun) almost always go before the noun:

głośny film – a loud film
dobry film – a good film
nowy samochód – a new car

film głośny would typically be understood as a predicative structure, like:

Film jest głośny. – The film is loud.
In poetry or special emphasis you might see: Film, głośny i męczący, trwał trzy godziny.

In our sentence, głośny simply describes what kind of film they are watching, so the normal order is głośny film.

Logically, the sound is loud, not the film. Is it natural in Polish to say głośny film?

Yes, it’s completely natural and idiomatic. Polish often attributes properties to the source of the sound:

głośny film – a loud movie (i.e. played very loud)
głośna muzyka – loud music
głośne radio – a loud radio

It’s understood that the sound produced by the film/music/radio is loud. You could also say:

oglądają film zbyt głośno – they are watching the film too loudly

but głośny film is the usual shorthand way to say it.

Why is the verb oglądają in the present tense if we’re describing a repeated situation?

Polish uses the present tense to talk about:

What is happening right now.
Habitual / repeated actions (like English “I usually…” / “I often…”).

Here, the sentence describes a general, repeated problem:

Wieczorem trudno mi zasypiać, gdy sąsiedzi oglądają głośny film.
= In the evenings it’s hard for me to fall asleep when the neighbors (tend to) watch a loud film.

This is the same use of present as in:

Kiedy piję kawę wieczorem, trudno mi zasnąć. – When I drink coffee in the evening, it’s hard to fall asleep.

So the simple present oglądają is the correct choice for a habitual situation.

Can I move mi or other elements around? For example, is Wieczorem mi trudno zasypiać OK?

Word order in Polish is fairly flexible, but there are preferences.

Most natural here:

Wieczorem trudno mi zasypiać.

Possible, but with slightly different emphasis:

Wieczorem mi trudno zasypiać.
→ extra focus on mi (to me), e.g. in contrast to someone else.
Mi wieczorem trudno zasypiać.
→ starts with mi, strong emphasis: As for me, in the evening it’s hard to fall asleep.

Grammatically these are okay, but the neutral, most typical version is the one given in the original sentence.