Learn Hardcore Indonesian: Ketika dia tersenyum, wajah dia kelihatan bahagia. - When he/she smiles, his/her face looks happy.

The tense is understood from context or from extra time words like tadi (earlier), kemarin (yesterday), nanti (later), etc. The verb forms tersenyum and kelihatan themselves are neutral for tense.

What is the difference between ketika, saat, and waktu for “when”?

All three can introduce a time clause and are often interchangeable:

ketika – a bit more formal/neutral, common in writing: Ketika dia tersenyum…
saat – also common and neutral, slightly more colloquial: Saat dia tersenyum…
waktu – literally “time”, but also used as “when” in speech: Waktu dia tersenyum…

In everyday conversation saat and waktu are very frequent. In more careful writing, ketika is very common.

Why is it wajah dia and not wajahnya? Which one is more natural?

Both are grammatically correct, but wajahnya is usually more natural here:

wajah dia = his/her face (literally: face he/she)
wajahnya = his/her face (-nya is a possessive suffix: his/her/its/their)

Most native speakers would probably say:
Ketika dia tersenyum, wajahnya kelihatan bahagia.

wajah dia tends to sound a bit more explicit or slightly less smooth in this context.

Can I drop the second dia and just say wajahnya kelihatan bahagia?

Yes. Once it’s clear who you’re talking about, you can say:

Ketika dia tersenyum, wajahnya kelihatan bahagia.

Here, -nya on wajahnya already refers back to dia, so you don’t need dia again. If the context is clear, you could even drop the first dia in speech:

Ketika tersenyum, wajahnya kelihatan bahagia.

But the original version with dia is very clear for learners.

What does the ter- in tersenyum mean? Is senyum also a verb?

The root is senyum (a smile). With ter-, tersenyum is the standard verb to smile.

senyum alone can be used as a casual verb in speech: Dia senyum. (He/She smiles.)
tersenyum is the more standard/neutral form: Dia tersenyum.

In many words, ter- has meanings like “accidental”, “in a state of”, or a passive sense, but for tersenyum it’s just the normal verb form “to smile”.

What is the difference between kelihatan, terlihat, and tampak?

All three can mean to look / to seem / to appear (visually):

kelihatan – very common and neutral: wajahnya kelihatan bahagia
terlihat – a bit more formal/literary: wajahnya terlihat bahagia
tampak – also “seems/appears”, slightly more formal or descriptive: wajahnya tampak bahagia

In everyday conversation, kelihatan is probably the most frequent; in writing you often see terlihat and tampak too.

Why do we say wajah dia kelihatan bahagia instead of just dia kelihatan bahagia?

Both are possible, but they focus on different things:

Dia kelihatan bahagia. – He/She looks happy (overall impression).
Wajah dia kelihatan bahagia. – His/Her face looks happy (specifically the face, facial expression).

The original sentence emphasizes that the face shows happiness when he/she smiles.

What is the nuance of bahagia compared to senang or gembira?

All can translate as happy, but with slightly different nuances:

bahagia – deeper, more complete happiness (content, fulfilled); often used for long‑term or meaningful happiness (marriage, life, family).
senang – pleased, glad, happy about something; often more casual/short‑term.
gembira – joyful, cheerful, often energetic happiness.

In this sentence, bahagia suggests that the face shows a real, genuine happiness, not just a brief pleased reaction.

Is the comma after tersenyum necessary in Indonesian?

In writing, it is standard and recommended to put a comma after a dependent time clause at the beginning:

Ketika dia tersenyum, wajahnya kelihatan bahagia.

In speech you just make a natural pause. Grammatically, the sentence would still be understandable without the comma, but proper writing normally includes it.

Does dia mean “he” or “she”? How do you show gender in Indonesian?

dia can mean he or she; it is gender‑neutral. Indonesian usually does not mark gender in pronouns.

If you need to be explicit, you can add words like:

pria / laki-laki – male
wanita / perempuan – female

For example: Pria itu tersenyum, wajahnya kelihatan bahagia. = That man smiled; his face looked happy.

Is this sentence formal, informal, or neutral? Are there more casual alternatives?

The sentence is neutral and fine in both spoken and written Indonesian.

More casual variants might be:

Pas dia senyum, mukanya kelihatan bahagia.
- pas instead of ketika (more colloquial “when/as soon as”)
- senyum instead of tersenyum
- muka instead of wajah (more colloquial for “face”)

The original version is appropriate in most situations, including polite conversation and writing.