Nije važno tko je bio kriv; važnije je da jedno drugome oprostimo.

Because Croatian often uses the neuter singular in impersonal statements like:

• Važno je... = It is important...
• Dobro je... = It is good...
• Teško je... = It is hard...

Here, the thing being described is not a noun like problem or odluka, but a whole clause:

• tko je bio kriv
• da jedno drugome oprostimo

So Croatian uses the neuter singular predicative form: važno and its comparative važnije.

In standard Croatian, tko is the normal word for who.

• Tko je došao? = Who came?
• Tko je bio kriv? = Who was at fault?

You may hear ko in colloquial speech or in other varieties of the language, but tko is the standard Croatian form.

Because tko is grammatically treated as masculine singular when the person’s gender is unknown or not specified.

So Croatian says:

• Tko je bio kriv?
• Tko je došao?
• Tko je spreman?

This does not mean the person was male. It is just the default grammatical form. If you later name a woman, you would switch to feminine:

• Ana je bila kriva.

Bio makes the clause clearly refer to a past situation:

• tko je bio kriv = who was at fault / who was to blame

If you say:

• tko je kriv

that usually means who is at fault now, or it sounds more present/general.

So bio matches the idea that the blame belongs to some earlier event or argument.

Here da introduces a clause meaning something like:

• that we forgive each other
• for us to forgive each other

After words like važno, potrebno, dobro, bolje, Croatian very often uses da + present tense where English might use either:

• a that-clause
• or an infinitive with to

So:

• Važnije je da oprostimo. = It is more important that we forgive.

An infinitive is also possible in some cases, but da + verb is extremely common and natural.

Formally, oprostimo is the 1st person plural form of oprostiti. In this sentence, because it follows da, it is understood as part of a da-clause, not as a command.

So here it means:

• that we forgive
• that we should forgive

not:

• let’s forgive!

Without da, the same form could be imperative-like:

• Oprostimo i krenimo dalje. = Let’s forgive and move on.

So the surrounding structure tells you how to read it.

This is an aspect difference.

• oprostiti = perfective, to forgive fully / to reach forgiveness
• opraštati = imperfective, to be forgiving / to forgive repeatedly or as an ongoing process

In this sentence, the focus is on the result: reaching forgiveness. That is why oprostimo is natural.

If you used opraštamo, it would sound more like an ongoing or habitual action, which does not fit as well here.

It means each other or one another.

Croatian does not have one single fixed word that works exactly like English each other. Instead, it uses expressions built from jedan + drugi, and the form changes depending on grammar.

Here:

• jedno drugome = to each other

This kind of expression is very common when talking about a pair of people.

Compare:

• Vole jedno drugo. = They love each other.
• Pišu jedno drugome. = They write to each other.

Because the verb oprostiti normally takes the person in the dative:

• oprostiti komu = to forgive someone

So in this sentence:

• drugome is dative
• the whole phrase jedno drugome means to each other

You can think of it literally as something like one to the other.

Because Croatian usually drops subject pronouns when the verb ending already shows who the subject is.

The ending -mo in oprostimo already tells you it means we.

So mi is unnecessary unless you want emphasis or contrast:

• ...da mi oprostimo, a ne oni. = ...that we forgive, not they.

This is very normal in Croatian.