Perjalanan pulang saya agak lama kerana jalan sesak.

In Malay, the possessor usually comes after the noun, not before it.

So:

• perjalanan pulang saya = my journey home
• literally: journey home my

This is very normal Malay word order. English says my journey, but Malay usually says journey my.

Perjalanan means journey, trip, or travel.
Pulang means to go home or to return home.

Together, perjalanan pulang means:

• the journey home
• the return trip home

So pulang is describing what kind of journey it is: a homeward journey.

Because pulang belongs with perjalanan, not with saya.

The structure is:

• perjalanan pulang = journey home
• perjalanan pulang saya = my journey home

So first you build the noun phrase perjalanan pulang, then you add the possessor saya.

If you moved saya earlier, the meaning or structure would become awkward.

Usually no, not for this meaning.

Perjalanan saya pulang sounds unnatural if you want to say my journey home.
Malay prefers perjalanan pulang saya because pulang directly modifies perjalanan.

Think of it as:

• correct/natural: perjalanan pulang saya
• not the normal way for this meaning: perjalanan saya pulang

Agak means rather, quite, fairly, or somewhat.

So:

• agak lama = rather long
• fairly long
• quite a long time

It softens the statement a little. It is not as strong as saying something was very long.

For comparison:

• lama = long
• agak lama = rather/fairly long
• sangat lama = very long

Here it means long in the sense of taking a long time.

Lama can mean different things depending on context:

• rumah lama = old house
• lama menunggu = waited a long time
• perjalanan ... lama = the journey was long / took a long time

In this sentence, because it is talking about a journey, lama clearly means it took a long time.

Malay often does not use a verb like English is/was/are/were in simple descriptive sentences.

So:

• Perjalanan pulang saya agak lama
  literally: My journey home rather long
• natural English: My journey home was rather long

This is completely normal in Malay.
You do not need a word equivalent to was here.

Yes, both can mean because.

• kerana = because
• sebab = because / because of / reason

In many everyday situations, sebab is very common and conversational.
Kerana often sounds a little more standard or formal.

So these are both natural:

• Perjalanan pulang saya agak lama kerana jalan sesak.
• Perjalanan pulang saya agak lama sebab jalan sesak.

Both mean essentially the same thing.

Literally:

• jalan = road
• sesak = crowded, packed, congested

So jalan sesak means the roads were congested or traffic was heavy.

In context, it refers to road congestion / traffic jams, not that the road is physically small.

A very natural English translation would be:

• because the traffic was bad
• because the roads were congested

Malay often uses shorter expressions when the meaning is clear from context.

• jalan sesak = the roads are congested
• jalan raya sesak = the roads/highways are congested
• lalu lintas sesak = traffic is congested

All of these can work, but jalan sesak is a compact, natural way to express the idea.

Depending on context, a speaker may also say:

• trafik sesak
• lalu lintas sesak

These are just different ways of talking about traffic congestion.

Malay does not usually use articles like English a, an, and the.

So Malay can say:

• perjalanan pulang saya = my journey home
• jalan sesak = the roads were congested / roads were congested

English requires articles much more often, but Malay usually leaves them out unless some other word makes the meaning specific.

Yes. It follows very normal Malay patterns.

The sentence breaks down like this:

• Perjalanan pulang saya = subject noun phrase
• agak lama = description/predicate
• kerana jalan sesak = reason clause

So the overall pattern is:

• [subject] + [description] + [reason]

This is a very common Malay structure.

Yes. A more casual version might be:

• Perjalanan balik saya agak lama sebab jalan sesak.

Differences:

• pulang and balik can both relate to returning; balik is often more conversational
• sebab is often more conversational than kerana

So:

• Perjalanan pulang saya agak lama kerana jalan sesak.
  sounds standard and natural
• Perjalanan balik saya agak lama sebab jalan sesak.
  sounds a bit more everyday and spoken

Both are understandable and natural.