Kerosakan kenderaan itu serius.

Malay often leaves out the present-tense to be when linking a subject to an adjective or noun.

So:

Kerosakan kenderaan itu serius.

naturally means:

The damage to the vehicle is serious.

You do not normally need a separate word for is here.

Kerosakan is a noun meaning damage, breakdown, fault, or malfunction, depending on context.

It comes from the root rosak, which usually means broken, damaged, or spoiled.

A useful way to think of it is:

• rosak = damaged / broken
• kerosakan = damage / breakdown

So the sentence uses the noun kerosakan, not the adjective rosak.

In Malay, noun phrases are often built with the main noun first, followed by the word or phrase that specifies it.

So:

• kerosakan kenderaan itu = the damage of/to that vehicle

This is normal Malay structure.

It may feel reversed compared with English, but it is very common:

• rumah Ali = Ali's house
• warna kereta itu = the colour of that car
• kerosakan kenderaan itu = the damage to that vehicle

Because demonstratives like ini and itu normally come after the noun in Malay.

So:

• kenderaan itu = that vehicle
• rumah itu = that house
• buku ini = this book

This is one of the most important word-order differences from English.

Literally, itu means that. But in actual use, it can also make the noun phrase feel definite, so in many contexts it can sound like the in English.

So kenderaan itu may be understood as:

• that vehicle
• the vehicle

The best translation depends on context.

Because serius is the predicate adjective.

The structure is:

• Kerosakan kenderaan itu = the subject
• serius = what is being said about the subject

Malay commonly puts the adjective in this position when it functions like is serious in English.

So the pattern is basically:

[subject] + [adjective]

For example:

• Cuaca panas. = The weather is hot.
• Keadaan itu sukar. = That situation is difficult.
• Kerosakan kenderaan itu serius. = The damage to the vehicle is serious.

It is most naturally understood as singular here: vehicle.

Malay nouns usually do not change form for plural the way English nouns do. Context normally tells you whether something is singular or plural.

If a speaker really wants to make it clearly plural, they might use:

• kenderaan-kenderaan = vehicles

But in your sentence, kenderaan is most likely just vehicle.

It can mean either, depending on context.

With kenderaan, kerosakan may refer to:

• physical damage
• a fault
• a mechanical problem
• a breakdown

So the sentence could refer to severe accident damage, or to a serious malfunction. The wider situation would tell you which meaning is intended.

Yes, if you specifically mean a car.

• kenderaan = vehicle
• kereta = car

So:

• Kerosakan kenderaan itu serius. = The damage to that vehicle is serious.
• Kerosakan kereta itu serius. = The damage to that car is serious.

Use kenderaan when you want a broader or more formal word.

Yes. A very natural alternative is:

Kerosakan pada kenderaan itu serius.

Here, pada makes the relationship more explicit:

• kerosakan pada kenderaan itu = damage to that vehicle

Another possible rewording is:

Kenderaan itu mengalami kerosakan serius.

This means:

• That vehicle has serious damage
• That vehicle has suffered serious damage

All of these are natural, but your original sentence is already correct.