W sobotę idziemy do biblioteki razem.

Because after w when talking about on a particular day, Polish uses the accusative case.

• basic form: sobota = Saturday
• accusative form: sobotę

So:

• w sobotę = on Saturday

This is a very common pattern with days of the week:

• w poniedziałek = on Monday
• we wtorek = on Tuesday
• w środę = on Wednesday
• w sobotę = on Saturday

So the ending changes because the noun is not in its dictionary form here.

Idziemy means we go / we are going.

It comes from the verb iść, which is used for going in one direction or for a specific trip. In this sentence, it suggests a concrete plan or movement:

• idziemy do biblioteki = we are going to the library

This is different from chodzimy, which usually means we go regularly / we walk around / we attend habitually.

Compare:

• Idziemy do biblioteki = We are going to the library.
• Chodzimy do biblioteki = We go to the library regularly.

Because the preposition do requires the genitive case.

• dictionary form: biblioteka = library
• genitive form: biblioteki

So:

• do biblioteki = to the library

This is a very important Polish rule: many prepositions force a particular case, and do almost always takes the genitive.

Other examples:

• do domu = to the house / home
• do szkoły = to school
• do sklepu = to the shop

In Polish, do often expresses movement to / into a place.

So:

• iść do biblioteki = to go to the library
• jechać do Warszawy = to go to Warsaw
• wracać do domu = to return home

English uses to, but Polish often uses do + genitive for movement toward a destination.

Grammatically, idziemy is present tense. But in real use, Polish often uses the present tense to talk about a planned future action, especially when there is a time expression.

Since the sentence begins with W sobotę (On Saturday), the meaning is naturally future:

• W sobotę idziemy do biblioteki razem.
  = On Saturday we’re going to the library together.

English does something similar with We’re going on Saturday.

Because Polish has no articles. There is no direct equivalent of a/an/the.

So biblioteka can mean:

• a library
• the library

The exact meaning depends on context.

In this sentence, English would usually translate it as the library, but Polish does not need a separate word for that.

Razem means together.

• idziemy do biblioteki razem = we are going to the library together

It is not grammatically necessary if the context already makes it obvious, but it adds useful information or emphasis. Without it:

• W sobotę idziemy do biblioteki. = On Saturday we’re going to the library.

With razem, the sentence clearly says that the people are going together, not separately.

Yes. Polish word order is more flexible than English word order because the cases show the grammatical relationships.

The sentence:

• W sobotę idziemy do biblioteki razem.

is a natural, neutral order. But other orders are possible, depending on emphasis:

• Razem idziemy do biblioteki w sobotę.
• Do biblioteki idziemy razem w sobotę.
• W sobotę razem idziemy do biblioteki.

These all mean roughly the same thing, but the focus changes a little. The original version sounds very natural and straightforward.

Most naturally, w sobotę means on Saturday or this Saturday, depending on context.

In this sentence, it usually sounds like a specific Saturday, especially because idziemy suggests a plan.

If you want to say every Saturday, Polish more often uses:

• w soboty = on Saturdays
• co sobotę = every Saturday

So:

• W sobotę idziemy do biblioteki. = On Saturday we’re going to the library.
• W soboty chodzimy do biblioteki. = We go to the library on Saturdays.

Because Polish verbs usually already show the subject.

The ending -emy in idziemy tells you the subject is we.

So Polish often does not need the pronoun my (we).

• idziemy = we go / we are going

You can add my for emphasis:

• My idziemy do biblioteki razem. = We are the ones going to the library together.

But in a normal sentence, leaving out my is more natural.

A useful approximate pronunciation is:

• sobotę ≈ so-BO-teh with a nasal ending

The letter ę is a nasal vowel, but at the end of a word many speakers pronounce it less strongly nasally, often somewhat like e with a slight nasal quality.

So for learners, a good practical goal is:

• don’t pronounce it like plain English ay
• aim for something close to eh, with a light nasal sound if possible

You do not need perfect nasal vowels right away to be understood, but it is good to notice that ę is not the same as plain e.

Yes, it is natural and correct.

A very natural English equivalent would be:

• On Saturday we’re going to the library together.

The sentence sounds like a normal statement about a plan. Its structure is simple and common:

• time expression: W sobotę
• verb: idziemy
• destination: do biblioteki
• manner / accompaniment idea: razem

So it is a good model sentence for learning several basic Polish patterns at once.