Dia is a gender‑neutral third-person singular pronoun. It can mean:
Malay usually does not mark gender unless you add extra words like lelaki (male) or perempuan (female). So Dia mengaku bahawa itu salah dia can be:
The context tells you which one is intended.
The two dia have different functions:
The first Dia is the subject (the one doing the action):
The second dia shows possession in salah dia (literally fault of him/her):
Malay often uses a pronoun after a noun to show possession:
So the literal structure is like:
He/She admitted that that was fault of him/her.
Bahawa is a conjunction that introduces a content clause, similar to that in English:
You can often omit bahawa, especially in spoken Malay:
This is still correct and natural in everyday conversation.
Rough guideline:
In many cases bahawa and that in English behave similarly: both are often optional.
They are related but not the same:
aku
mengaku
mengakui
In your sentence, mengaku is the natural choice:
Itu generally means that or it, and ini means this.
In this sentence:
Itu refers to a previously mentioned action or situation (something already known in the context). Using itu is natural when talking about:
Ini salah dia = this is his/her fault
So in most contexts of admitting blame for something that happened, itu is preferred.
Salah in Malay can be both:
Adjective: wrong / incorrect / mistaken
Noun: fault / mistake / wrongdoing
In salah dia, salah behaves more like a noun: fault / mistake.
You can see this more clearly in a more obviously nominal version:
So:
Yes, you can say:
This is more literally:
Meaning-wise, it is very close to:
Subtle nuance:
In most everyday contexts, both will be understood as an admission of fault and are more or less interchangeable.
Both are correct, but there is a difference in feel:
salah dia
kesalahan dia
Your sentence:
Malay verbs like mengaku do not change form to show tense. There are no endings like -ed, -s, or will built into the verb.
Dia mengaku bahawa itu salah dia can potentially mean:
Which tense is intended depends on:
Examples:
Semalam dia mengaku bahawa itu salah dia.
= Yesterday he/she admitted it was his/her fault.
Dia akan mengaku bahawa itu salah dia.
= He/She will admit that it is his/her fault.
Without context, English speakers usually translate this sentence in the past tense because admitting fault is usually about something that already happened.
The sentence is neutral and suitable in most situations. It’s not slangy, and not extremely formal either.
Some variations by register:
More casual / spoken:
More formal:
But Dia mengaku bahawa itu salah dia is perfectly fine and widely understood.
Approximate syllable breakdown and stress (Malay stress is light and usually near the end):
Spoken smoothly:
In casual speech, bahawa may be pronounced quickly, almost like baha or bawa, but in careful speech you keep all three syllables ba-ha-wa.