W niedzielę w mieście jest mniej ludzi.

Because the two w phrases do two different jobs:

• w niedzielę = on Sunday
• w mieście = in the city

So it is not repetitive in a bad way; Polish simply uses the same preposition w for both a time expression and a place expression here.

Niedziela is the dictionary form, or nominative.

After w in this kind of time expression with days of the week, Polish uses the accusative:

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

So w niedzielę is just the correct case form after the preposition in this expression.

Because after w when it means in a place, Polish uses the locative case.

• miasto = city, town
• w mieście = in the city / in town

So the noun changes form:

• miasto → mieście

This is a normal case change after w for location.

Because mniej normally requires the genitive case.

So:

• ludzie = people, the nominative form
• mniej ludzi = fewer people

The same thing happens with other quantity words:

• dużo ludzi = many people
• mało czasu = little time
• więcej pieniędzy = more money

So after mniej, ludzi is the expected form.

This is a very common question.

In Polish, expressions with quantity words like dużo, mało, mniej, and więcej often take singular neuter-style agreement in existential sentences:

• jest mniej ludzi
• było dużo gości
• będzie więcej samochodów

So even though the meaning involves many people, the grammar is built around the quantity expression mniej ludzi, and the verb is usually jest, not są.

If the subject were plain ludzie, then you would use są:

• Ludzie są w mieście = The people are in the city

But here the structure is different: there are fewer people, so jest mniej ludzi is normal.

Polish usually does not need a separate word for there in this kind of sentence.

English says:

• There are fewer people in the city on Sunday

Polish simply says:

• W niedzielę w mieście jest mniej ludzi

Here jest carries the idea of existence, so the whole phrase means something like there is/are fewer people. This is very natural in Polish.

It can mean either, depending on context.

• W niedzielę can mean on Sunday in a specific situation.
• It can also mean on Sundays as a general statement.

So W niedzielę w mieście jest mniej ludzi can mean:

• There are fewer people in the city on Sunday
• or There are fewer people in the city on Sundays

If you want to be more specific, Polish can make that clearer:

• w tę niedzielę = this Sunday
• w każdą niedzielę = every Sunday

Yes. Polish word order is fairly flexible, because the case endings show how the words relate to each other.

The sentence as given is very natural:

• W niedzielę w mieście jest mniej ludzi.

But you can move things for emphasis, for example:

• W mieście jest mniej ludzi w niedzielę.
• Mniej ludzi jest w mieście w niedzielę.

These versions are grammatically possible, but the emphasis changes. The original sentence sounds neutral and natural if you want to start with the time phrase on Sunday.

Yes, absolutely.

• mniej ludzi
• mniej osób

Both mean fewer people.

There is a slight difference in feel:

• ludzie / ludzi is the everyday word for people
• osoby / osób can sound a bit more neutral, formal, or impersonal

So both are correct, but mniej ludzi sounds very natural in everyday speech.

Polish has no articles like the or a, so w mieście can match several English translations depending on context:

• in the city
• in a city
• in town

In this sentence, English will often use in the city or in town, depending on the situation.

So the Polish phrase itself does not mark the difference between the and a. Context tells you which English version fits best.

No, not quite.

• w mieście usually means physically in the city / in town
• na mieście often means out in town, especially socially, like being out in cafés, bars, shops, or the center

So in your sentence, w mieście is the right choice because it is simply about how many people are present in the city.

If you said na mieście, it would suggest a slightly different idea, more like being out and about in town.