Jeśli egzemplarz jest niedostępny, nie mogę go wypożyczyć.

Not exactly. Egzemplarz means a copy or a specific экземпляр/item instance of something, especially in a library, shop, or archive.

In a library sentence like this, egzemplarz usually means a particular copy of a book rather than the title in general.

So:

• książka = book
• egzemplarz książki = a copy of a book

That is why this sentence sounds natural in a library context.

Jeśli means if.

It introduces a condition:

• Jeśli egzemplarz jest niedostępny... = If the copy is unavailable...

You may also see jeżeli, which also means if and is slightly more formal or neutral in some contexts. In everyday Polish, jeśli is very common.

Because Polish normally uses a comma to separate a subordinate clause from the main clause.

Here the first part is the condition:

• Jeśli egzemplarz jest niedostępny

and the second part is the main statement:

• nie mogę go wypożyczyć

So the comma is standard Polish punctuation after an if-clause.

Because niedostępny is an adjective and it has to agree with egzemplarz.

• egzemplarz is masculine singular
• so the adjective is also masculine singular: niedostępny

Compare:

• egzemplarz jest niedostępny = the copy is unavailable
• książka jest niedostępna = the book is unavailable
• wydanie jest niedostępne = the edition is unavailable

The ending changes to match the noun’s gender and number.

It literally means unavailable or not available.

It is built from:

• dostępny = available, accessible
• nie- = not

So:

• dostępny = available
• niedostępny = unavailable

In this sentence it most likely means the library copy cannot currently be borrowed or accessed.

Because jest is the 3rd person singular form of być = to be.

So:

• egzemplarz jest niedostępny = the copy is unavailable

In present-tense Polish, when you say that someone or something is something, you normally use the present form of być.

Here:

• jest = is

Mogę is the 1st person singular present form of móc = can / be able to.

So:

• mogę = I can
• nie mogę = I cannot / I can’t

This verb is irregular, so its forms are worth memorizing:

• mogę = I can
• możesz = you can
• może = he/she/it can
• możemy = we can
• możecie = you can
• mogą = they can

Go means him/it in the accusative, and here it means it.

It refers back to egzemplarz:

• egzemplarz = copy
• go = it

So:

• nie mogę go wypożyczyć = I can’t borrow it

Polish often uses object pronouns where English would use it, and go is the correct form here because wypożyczyć takes a direct object in the accusative.

Because go is the object form needed after the verb wypożyczyć.

You are borrowing something, so that thing is the direct object.

• nominative: egzemplarz
• accusative replacement pronoun: go

To usually means this/it in a different grammatical role, not the normal direct-object pronoun here.

So:

• Nie mogę go wypożyczyć = correct
• Nie mogę to wypożyczyć = not correct in standard Polish

Because short object pronouns in Polish often appear before the infinitive or before the main verbal part of the predicate.

So this is natural:

• nie mogę go wypożyczyć

This word order is very common and neutral.

Polish word order is flexible, but go before the infinitive sounds most natural here.

Wypożyczyć means to borrow or sometimes to loan out, depending on context.

In a library sentence with I, it means to borrow:

• wypożyczyć książkę = to borrow a book

Be careful: in Polish, wypożyczyć can sometimes be used from either side of the transaction depending on context, but in library usage wypożyczyć very often means borrow/check out.

This is about aspect.

• wypożyczyć = perfective
• wypożyczać = imperfective

Here, the perfective form is natural because it refers to a complete action: to borrow/check out the copy.

So:

• nie mogę go wypożyczyć = I can’t borrow it / I can’t check it out

If you used wypożyczać, it would sound more like an ongoing, repeated, or general process.

A learner-friendly way to think about it:

• wypożyczyć = borrow it successfully as one completed action
• wypożyczać = be borrowing / borrow repeatedly / borrow in general

Polish negates verbs with nie, written separately from the finite verb:

• mogę = I can
• nie mogę = I cannot

This is very standard:

• mam = I have
• nie mam = I do not have
• widzę = I see
• nie widzę = I do not see

So in this sentence:

• nie mogę go wypożyczyć = I can’t borrow it

Yes. Polish word order is more flexible than English.

For example, you could also say:

• Nie mogę go wypożyczyć, jeśli egzemplarz jest niedostępny.

That still means the same thing: I can’t borrow it if the copy is unavailable.

The original version is very natural because it presents the condition first and then the result.

Sometimes Polish allows the object to be omitted if it is obvious from context, but in this sentence go is very natural and helpful.

• Nie mogę wypożyczyć by itself sounds incomplete unless the listener already knows exactly what you mean.
• Nie mogę go wypożyczyć clearly says I can’t borrow it.

So including go is the normal choice here.