Dis nie dat biblioteekeksemplare verdwyn nie—dis net dat leesdoelwitte verander.

Dis is the very common contracted form of Dit is, meaning it is.

So:

• Dis nie ... nie = It is not ...
• Dis net dat ... = It’s just that ...

You could write the sentence more fully as:

• Dit is nie dat biblioteekeksemplare verdwyn nie—dit is net dat leesdoelwitte verander.

In everyday Afrikaans, dis is extremely common in both speech and writing.

Afrikaans normally uses double negation.

In a basic negative clause, you usually get:

• one nie earlier in the clause
• another nie near the end of the clause

So:

• Dis nie dat biblioteekeksemplare verdwyn nie = It’s not that library copies are disappearing

This double-nie pattern is one of the most important features of Afrikaans grammar. English speakers often want to use just one negative word, but standard Afrikaans usually needs both.

Dat here means that and introduces a subordinate clause.

So:

• dis nie dat ... nie = it’s not that ...
• dis net dat ... = it’s just that ...

The sentence has two dat-clauses:

• dat biblioteekeksemplare verdwyn
• dat leesdoelwitte verander

Each one explains what is being denied or explained.

Because after dat, Afrikaans uses subordinate clause word order, where the verb typically goes to the end.

Compare:

• Main clause: Leesdoelwitte verander. = Reading goals change.

• Subordinate clause: ... dat leesdoelwitte verander. = ... that reading goals change.

The same thing happens in:

• dat biblioteekeksemplare verdwyn

For English speakers, this is very worth noticing: after words like dat, Afrikaans often pushes the verb to the end.

Yes. Afrikaans, like Dutch and German, very often forms compound nouns as a single word.

So:

• biblioteek = library
• eksemplaar = copy
• biblioteekeksemplaar = library copy
• biblioteekeksemplare = library copies

English often writes these as separate words, but Afrikaans usually joins them.

Eksemplare is the plural of eksemplaar.

So:

• singular: eksemplaar
• plural: eksemplare

Not all Afrikaans plurals take -s. Some nouns take -e, and some have spelling changes as well. This is one you simply learn as a vocabulary item:

• ’n biblioteekeksemplaar = a library copy
• biblioteekeksemplare = library copies

Because the sentence is talking about those things in general, not about specific ones.

So:

• biblioteekeksemplare verdwyn = library copies disappear / are disappearing
• leesdoelwitte verander = reading goals change / are changing

This is similar to English generic plurals, where you can also say:

• Books are expensive
• Goals change

without the.

Here net means just, simply, or merely.

So:

• dis net dat leesdoelwitte verander = it’s just that reading goals change

It softens and clarifies the statement. The speaker is saying:

• The issue isn’t X; it’s simply Y.

Afrikaans net is very common and often corresponds to English just.

Yes, absolutely.

These are the same in meaning:

• Dis nie dat ... dis net dat ...
• Dit is nie dat ... dit is net dat ...

The version with dis is more natural in everyday use. The full form dit is can sound slightly more formal or more emphatic, depending on context.

Yes. Verdwyn is present tense, but like many present-tense forms in Afrikaans, it can be translated in more than one way depending on context.

So:

• biblioteekeksemplare verdwyn could be understood as
  • library copies disappear
  • library copies are disappearing

Likewise:

• leesdoelwitte verander could mean
  • reading goals change
  • reading goals are changing

English chooses between simple present and present progressive more often than Afrikaans does.

The dash separates two contrasting parts of the statement:

• It’s not that X ...
• it’s just that Y ...

So it helps show the correction or contrast very clearly.

You could also see a comma in similar sentences, but the dash gives a slightly stronger pause and emphasis. It signals something like:

• Not this explanation—rather this one.

It uses a very common contrast-and-correction pattern:

• Dis nie dat X nie—dis net dat Y.

This pattern is useful when you want to reject one explanation and offer another.

For example:

• Dis nie dat hy onbeskof is nie—dis net dat hy skaam is. = It’s not that he’s rude—it’s just that he’s shy.

• Dis nie dat die werk moeilik is nie—dis net dat dit lank vat. = It’s not that the work is difficult—it’s just that it takes a long time.

So the sentence you were given is a very good model for a useful real-life structure.