Dia mengemudi sembarangan di jalan gelap, jadi saya takut.

In Indonesian, dia is a third-person singular pronoun that can mean he or she. Indonesian usually does not mark gender in pronouns the way English does.

So:

• Dia mengemudi... = He is driving... or She is driving...

You only know the gender from context, or it may simply be unimportant.

Kemudi is related to steering or rudder, but mengemudi is the verb meaning to drive.

This is a common Indonesian pattern:

• a root or base idea
• plus the prefix meN- to form an active verb

So:

• mengemudi = to drive

A learner may also hear menyetir, which also means to drive. Both are used, though menyetir is very common in everyday speech.

Here, sembarangan means something like:

• carelessly
• recklessly
• without proper care
• in an irresponsible way

So mengemudi sembarangan means to drive carelessly/recklessly.

Be aware that sembarangan can have slightly different shades of meaning depending on context. It can also mean randomly, indiscriminately, or not properly. In this sentence, the natural meaning is recklessly/carelessly.

Because it is modifying the verb mengemudi. In Indonesian, adverb-like words often come after the verb.

So:

• mengemudi sembarangan = drive carelessly

This is very natural Indonesian word order.

Compare:

• berbicara pelan = speak softly
• jalan cepat = walk fast

So the pattern is often:

• verb + adverb/manner word

Literally, it means on a dark road or on a dark street.

Breakdown:

• di = in / at / on depending on context
• jalan = road / street
• gelap = dark

So:

• di jalan gelap = on a dark road

In English, we choose on because roads and streets usually take on, but Indonesian uses di much more broadly for location.

Because Indonesian often places adjectives directly after nouns.

So:

• jalan gelap = dark road
• literally, road dark

This is the normal pattern:

• rumah besar = big house
• mobil baru = new car
• jalan gelap = dark road

You do not need yang here.

Here, jadi means so, therefore, or as a result.

It connects the first clause to the second:

• Dia mengemudi sembarangan di jalan gelap, jadi saya takut.
• He/She was driving carelessly on a dark road, so I was afraid.

In other contexts, jadi can also mean:

• become
• turn into
• finished / done in some expressions

But here it is clearly a connector meaning so.

Because Indonesian often expresses feelings very simply.

• saya takut = I am afraid / I was afraid

You can say:

• saya merasa takut = I felt afraid

But it is not necessary. Indonesian often sounds more natural and direct with just:

• saya takut
• saya senang
• saya sedih

So saya takut is completely normal.

It can mean either one, depending on context.

Indonesian verbs do not change form for tense the way English verbs do. So Indonesian often leaves time unstated unless it is important or already clear from context.

That means:

• saya takut could mean I am afraid
• or I was afraid

The surrounding situation tells you which is intended.

If you want to make time clearer, Indonesian can add time words such as:

• tadi = earlier
• kemarin = yesterday
• sekarang = now

Because Indonesian does not usually use a verb like to be in the same way English does.

In English:

• I was afraid

In Indonesian:

• saya takut

No separate word for am/is/are/was/were is needed here.

This is a very common feature of Indonesian:

• Dia marah = He/She is angry
• Saya lelah = I am tired
• Mereka senang = They are happy

Yes. Takut can often be translated as:

• afraid
• scared
• sometimes fearful

The best English choice depends on context and style. In this sentence, both of these work well:

• so I was afraid
• so I was scared

Yes, it is understandable and natural. It clearly means that someone was driving recklessly on a dark road, and that caused the speaker to feel afraid.

A slightly different but also natural version could be:

• Dia mengemudi sembarangan di jalan yang gelap, jadi saya takut.

Adding yang is possible if you want to make dark feel a little more explicitly descriptive, but it is not required. The original sentence is fine.

Yes. For example:

• Budi mengemudi sembarangan di jalan gelap, jadi saya takut.
• Ia mengemudi sembarangan di jalan gelap, jadi saya takut.

Notes:

• dia is common and neutral in everyday use
• ia also means he/she, but it is a little more formal and is more common in writing than in casual speech

So dia is the most natural choice for everyday conversation.