W niedzielę lubię spokojne śniadanie na tarasie.

Niedziela is the basic dictionary form, called the nominative.

In this time expression, Polish uses w + accusative, so niedziela changes to niedzielę.

This is very common with days of the week:

• w sobotę — on Saturday
• w środę — on Wednesday
• w niedzielę — on Sunday

So this is something you will mostly learn as a pattern.

It can mean either, depending on context.

In this sentence, because the verb is lubię and the whole sentence sounds habitual, English will often translate it as on Sundays.

A few useful possibilities:

• w niedzielę — on Sunday / on Sundays
• w tę niedzielę — this Sunday
• w niedziele — on Sundays, with stronger emphasis on repetition

So here the meaning is probably habitual, not about one single Sunday.

After lubić, the thing you like is in the accusative case.

However, śniadanie is a neuter singular noun, and for many neuter nouns, the accusative looks exactly the same as the nominative.

So:

• nominative: śniadanie
• accusative: śniadanie

The case is still accusative grammatically, even though the form does not visibly change.

Because adjectives in Polish must agree with the noun in:

• gender
• number
• case

Śniadanie is:

• singular
• neuter
• accusative here

So the adjective must match it: spokojne

Compare:

• spokojny obiad — masculine
• spokojna kolacja — feminine
• spokojne śniadanie — neuter

It does not just mean calm in a literal emotional sense.

Here spokojne śniadanie suggests something like:

• peaceful
• relaxed
• unhurried
• leisurely

So it gives the feeling of a slow, pleasant breakfast, not a rushed one.

Because na can take different cases depending on meaning.

• na + accusative usually means movement toward a place
  
  • Idę na taras — I’m going onto the terrace
• na + locative usually means location
  
  • Jem na tarasie — I’m eating on the terrace

In your sentence, the breakfast happens there, so this is location, and Polish uses na tarasie.

Because Polish can use lubić directly with a noun.

So:

• Lubię kawę — I like coffee
• Lubię muzykę — I like music
• Lubię spokojne śniadanie na tarasie — I like a peaceful breakfast on the terrace

English often prefers I like having... or I like eating..., but Polish does not need that extra verb.

You could say Lubię jeść śniadanie na tarasie, but that focuses more on the activity of eating.

Because Polish has no articles.

There is no direct equivalent of English a, an, or the in normal Polish grammar.

So śniadanie can mean:

• breakfast
• a breakfast
• the breakfast

Context tells you which meaning is intended.

No. Polish word order is fairly flexible.

This sentence sounds natural because it starts with the time phrase w niedzielę, then gives the verb, then the thing liked, and finally the location.

This order is neutral and natural:

• W niedzielę lubię spokojne śniadanie na tarasie.

Other orders are possible, but they change emphasis:

• Spokojne śniadanie na tarasie lubię w niedzielę. — stronger focus on spokojne śniadanie na tarasie

So the original order is a very normal one, not the only one.