Kalau spion kotor, kita sulit melihat jalan di belakang.

Yes. Kalau here means if.

So Kalau spion kotor, ... = If the mirror is dirty, ...

A few useful notes:

• kalau is very common in everyday Indonesian
• it can also sometimes mean when depending on context
• a more formal alternative is jika

In this sentence, if is the best match.

Spion means a vehicle mirror, especially a rearview mirror or side mirror.

In everyday Indonesian, people often just say spion. You may also hear:

• kaca spion = mirror glass / car mirror
• spion mobil = car mirror
• spion motor = motorcycle mirror

So in this sentence, spion kotor means the mirror is dirty.

Because Indonesian often leaves out the verb to be in simple sentences.

So:

• spion kotor literally = mirror dirty
• natural English = the mirror is dirty

This is very normal in Indonesian. Some more examples:

• Rumah itu besar. = That house is big.
• Dia sakit. = He/She is sick.

So you should not expect a separate word for is every time.

This is a very common learner question.

• kita = we, including the listener
• kami = we, excluding the listener

In this sentence, kita is being used in a general sense, like English we in statements such as:

• If the mirror is dirty, we can’t see well
• We have trouble seeing the road behind

It can sound like a general human experience, not necessarily a specific group.

If you used kami, it would sound like we, but not you, which would be less natural here.

Sulit means difficult or hard.

In kita sulit melihat..., it means:

• it is hard for us to see...
• we have difficulty seeing...

A close everyday alternative is susah:

• kita sulit melihat = a bit more neutral or standard
• kita susah melihat = very common in speech

Both are natural, though sulit may sound slightly more standard.

Because melihat usually takes a direct object.

So:

• melihat jalan = see the road
• melihat mobil itu = see that car

You do not normally need ke before the thing being seen.

By contrast, ke is used more with direction, especially with look toward:

• melihat ke belakang = look to the back / look backward
• melihat ke kiri = look to the left

In your sentence, the object is jalan and di belakang describes which road:

• melihat jalan di belakang = see the road behind

Di belakang means behind or at the back.

It is written as two words because di here is a preposition showing location.

• di belakang = behind
• di rumah = at home
• di jalan = on the road

This is different from di- as a prefix for passive verbs, which is attached:

• ditulis = written
• dibuka = opened

So in this sentence, di belakang must be written separately.

Here, jalan most naturally means road.

But jalan is a flexible word. Depending on context, it can mean:

• road
• street
• way
• route

In melihat jalan di belakang, it refers to the roadway behind the vehicle.

Yes, jalan di belakang literally means the road behind.

Indonesian often leaves some relationships understood from context. Since the sentence is about a vehicle mirror, listeners naturally understand it as:

• the road behind us
• the road behind the vehicle

You could make it more explicit by saying:

• jalan di belakang kita = the road behind us
• jalan di belakang mobil = the road behind the car

But the original sentence is already natural and clear.

Yes, it is natural and understandable.

That said, native speakers might also say similar versions such as:

• Kalau spion kotor, kita sulit melihat jalan di belakang.
• Kalau kaca spion kotor, kita sulit melihat jalan di belakang.
• Kalau spion kotor, kita susah melihat jalan di belakang.

All of these are natural. The original sentence is perfectly fine.

The comma separates the if-clause from the main clause:

• Kalau spion kotor, = If the mirror is dirty,
• kita sulit melihat jalan di belakang. = we have difficulty seeing the road behind.

This is similar to English punctuation after an opening if clause.

In casual writing, people do not always use punctuation perfectly, but with standard writing, the comma is appropriate here.