Learn Hardcore Croatian: Za radoznale učenike nije bitno koliko je objašnjenje dugo, važno je da je jasno. - For curious pupils it is not important how long the explanation is; it is important that it is clear.

za + radoznale učenike = for curious students
Both radoznale and učenike are in accusative plural masculine (animate), agreeing with each other.

Why is it radoznale učenike and not radoznali učenici?

Because radoznali učenici is nominative (used for the subject), and here the phrase is part of a prepositional phrase with za, which requires the accusative.

Compare:

Radoznali učenici vole pitanja.
Curious students like questions.
(radoznali učenici = subject, nominative plural)
Za radoznale učenike nije bitno...
For curious students it is not important...
(za forces radoznale učenike into accusative plural)

The adjective radoznali changes to radoznale to agree with učenike in case (accusative), number (plural), and gender (masculine animate).

What is the subject of nije bitno and why is bitno in the neuter form?

Grammatically, the subject of nije bitno is the whole clause koliko je objašnjenje dugo (how long the explanation is).

In Croatian, when the subject is a whole clause (or something abstract like to = this/that/it), the predicate adjective typically goes into neuter singular:

Koliko je objašnjenje dugo nije bitno.
How long the explanation is does not matter.

Because that whole idea behaves like a neuter “it”, the adjective bitan (important) appears as bitno (neuter singular):

masculine: bitan
feminine: bitna
neuter: bitno

So nije bitno literally = is-not important (neuter) → does not matter.

How does the word order work in koliko je objašnjenje dugo?

The order follows two main rules:

The question word koliko (how much / how long) comes first.
The clitic je (is) must be in the second position within its clause.

In koliko je objašnjenje dugo:

koliko = 1st word
je = 2nd position (as required)
objašnjenje (subject)
dugo (predicate adjective: long, neuter to agree with objašnjenje)

So the underlying structure is:
koliko – je – objašnjenje – dugo

Literally: how long the explanation is.

Could I also say koliko je dugo objašnjenje, and is there any difference?

Yes, koliko je dugo objašnjenje is also correct and natural. The meaning is the same: how long the explanation is.

Two common variants:

koliko je objašnjenje dugo
koliko je dugo objašnjenje

Because Croatian word order is relatively flexible, you can move objašnjenje and dugo around, as long as:

koliko stays at the front of the clause, and
je stays in the clitic “second position” of that clause.

In everyday speech, Koliko je dugo objašnjenje? (as a direct question) is probably the most natural-sounding option, but the form used in your sentence is fully correct.

What exactly is the role of koliko here? Does it mean “how much” or “how long”?

Koliko is a general question word meaning how much / how many / how long. Its precise meaning is determined by context and the word it combines with.

With time and length, koliko + dugo commonly means how long (in time or in physical length):

Koliko je dugo objašnjenje? – How long is the explanation?
Koliko dugo traje objašnjenje? – How long does the explanation last?

In your sentence, koliko je objašnjenje dugo = how long the explanation is (its length or duration, depending on context).

Why do we have both bitno and važno? Aren’t they both “important”?

Bitan and važan are very close in meaning and can often be translated as important.

bitno (crucially / essentially important, relevant)
važno (important, significant)

In this sentence, the writer uses the near-synonyms to create a stylistic contrast:

nije bitno koliko je objašnjenje dugo
it is not important / it does not matter how long the explanation is

versus

važno je da je jasno
it is important that it is clear

So, bitno is used in the “this doesn’t matter” part, and važno in the “this does matter” part, which makes the contrast more vivid. Grammatically, both are neuter singular predicate adjectives.

Why is there a comma before važno je da je jasno and no conjunction like ali (but)?

Croatian allows two independent (main) clauses to be linked just with a comma, especially when the relationship between them is obvious from context.

Your sentence has two main clauses:

Za radoznale učenike nije bitno koliko je objašnjenje dugo,
važno je da je jasno.

You could also explicitly add a conjunction:

..., ali važno je da je jasno. – but it is important that it is clear.
..., samo je važno da je jasno. – only it is important that it is clear.

The comma alone suggests a contrast similar to but in English, and this is very common in written Croatian.

What does da do in važno je da je jasno?

Da introduces a subordinate clause that works like an English “that”-clause.

Važno je da je jasno.
Literally: Important is that it is clear.

Structure:

važno je – main clause (it is important)
da je jasno – subordinate da-clause expressing what is important (that it is clear)

This pattern is extremely common in Croatian:

Znam da je objašnjenje jasno. – I know that the explanation is clear.
Mislim da nije bitno. – I think (that) it is not important.

Why is je repeated in važno je da je jasno? Could we drop one of them?

You cannot drop either je here, because each clause needs its own verb biti (to be).

There are two separate clauses:

važno je – main clause (it is important)
da je jasno – subordinate clause (that it is clear)

Each clause must have its own je:

Važno je da jasno. – ungrammatical (no verb in the second clause)
Važno da je jasno. – colloquial, missing je in the main clause; you will hear it in speech but it’s not standard.

Standard written form keeps both: važno je da je jasno.

Why are so many words ending in -o: bitno, važno, jasno, dugo?

They are all neuter singular forms of adjectives used predicatively:

bitan – bitna – bitno (important)
važan – važna – važno (important)
dug – duga – dugo (long)
jasan – jasna – jasno (clear)

Neuter singular -o is used here because:

With abstract or clause subjects, Croatian typically uses neuter:
- Nije bitno. – It doesn’t matter.
- Važno je da je jasno. – It’s important that it is clear.
With a neuter noun like objašnjenje (the explanation), the predicate adjectives also take neuter:
- Objašnjenje je dugo i jasno. – The explanation is long and clear.

So -o is simply the neuter agreement marker.

Could we say Radoznalim učenicima nije bitno... instead of Za radoznale učenike nije bitno...?

Yes, that is possible and natural, but the nuance changes slightly.

Za radoznale učenike nije bitno...
Literally: For curious students, it is not important...
→ emphasizes them as the “target group” or for them, from their perspective.
Radoznalim učenicima nije bitno...
Dative plural (to curious students it is not important...)
→ emphasizes more directly to those students it is not important.

Both are fine and very close in meaning; za + accusative sounds a bit more generic/“for (the group)”, while bare dative can feel a bit more personal (to those students).

How do we know if objašnjenje means “the explanation” or “an explanation” in English?

Croatian has no articles (no a/an/the), so objašnjenje by itself can correspond to:

an explanation
the explanation
sometimes just explanation in an abstract sense

The exact English article is inferred from context. In this sentence, English prefers:

how long *the explanation is*
because we usually imagine a specific explanation being given.

If you really want to emphasize indefiniteness or definiteness in Croatian, you can optionally say:

jedno objašnjenje – one / an explanation
to objašnjenje – that/the explanation

But in normal speech, simple objašnjenje is enough.