Mereka berjuang untuk keadilan.

Yes. Mereka is the standard Malay third-person plural pronoun: they / them.

A few useful notes:

• It is not gendered. It can refer to men, women, or a mixed group.
• Malay does not distinguish they vs them in the same way English does, so mereka can work broadly depending on context.
• It is mainly used for people, not usually for things.

Berjuang means to struggle, to fight, or to strive for something.

It does not have to mean physical combat. It is often used in broader senses, such as:

• fighting for freedom
• struggling for rights
• striving for a goal
• campaigning for justice

So in this sentence, berjuang is probably about struggling or fighting in a moral, political, or social sense, not necessarily literal violence.

The prefix ber- often makes a word into an intransitive verb, often meaning:

• to do something
• to be engaged in something
• to have/use something, in other contexts

Here:

• root: juang = struggle/fight
• berjuang = to struggle / to fight

In this sentence, berjuang is an activity the subject is doing. It does not take a direct object in the same way an English verb like fight sometimes can.

Because berjuang normally does not take a direct object. It is typically followed by a phrase showing the goal or cause, often with a preposition like untuk.

So:

• berjuang untuk keadilan = fight/struggle for justice

If you want a more directly transitive structure, Malay often uses:

• memperjuangkan keadilan = to fight for / champion justice

So both are possible, but the grammar is different:

• berjuang untuk keadilan
• memperjuangkan keadilan

In this sentence, untuk means for in the sense of for the sake of or in support of.

So:

• untuk keadilan = for justice

It is true that untuk can also mean to or in order to in other sentences. Malay untuk is quite flexible, so context matters.

Here, because it is followed by keadilan (justice), the meaning is clearly for justice, not in order to justice.

Keadilan comes from:

• adil = fair, just
• ke-...-an = a circumfix that often creates an abstract noun

So:

• adil = just / fair
• keadilan = justice / fairness

This ke-...-an pattern is very common in Malay for abstract ideas. For example, it often turns an adjective or root into a noun referring to a quality or concept.

Usually justice is the best translation in this sentence.

But keadilan can overlap with:

• justice
• fairness
• equity, depending on context

In Mereka berjuang untuk keadilan, justice sounds most natural in English, especially if the context is rights, law, or social issues.

Malay verbs usually do not change form for tense the way English verbs do.

So berjuang by itself does not tell you whether the action is:

• present: they fight / are fighting
• past: they fought / were fighting
• future: they will fight

The time is usually understood from:

• context
• time words, such as semalam (yesterday), sekarang (now), esok (tomorrow)
• aspect markers like sedang, telah, akan

So without extra context, the sentence is tense-neutral.

Yes. This is a very normal Malay sentence pattern:

• Mereka = subject
• berjuang = verb
• untuk keadilan = prepositional phrase showing purpose/cause

So the basic order is:

Subject + Verb + Prepositional Phrase

That is very common in Malay and feels quite natural here.

Yes, absolutely.

Compare the two:

• Mereka berjuang untuk keadilan

  • literally: they struggle/fight for justice
  • focuses on the action of struggling, with untuk introducing the cause

• Mereka memperjuangkan keadilan

  • literally: they fight for / champion / advocate justice
  • more directly treats keadilan as the thing being fought for

In many contexts, both are natural.
A rough difference is:

• berjuang untuk... = more about engaging in a struggle
• memperjuangkan... = more about actively advocating or fighting for a particular cause

A simple approximate pronunciation is:

• Mereka ≈ muh-REH-kah
• berjuang ≈ ber-joo-AHNG
• untuk ≈ oon-TOOK
• keadilan ≈ kuh-ah-dee-LAN

A few helpful points:

• Malay pronunciation is usually more regular than English spelling.
• The r is usually lightly tapped or rolled.
• juang has two vowel sounds together, something like joo-ahng.
• Stress in Malay is generally not as strong or dramatic as in English.

So the whole sentence sounds roughly like:

muh-REH-kah ber-joo-AHNG oon-TOOK kuh-ah-dee-LAN