Learn Hardcore Indonesian: Serial dokumenter tentang iklim itu sederhana, tapi tetap menarik untuk ditonton malam hari. - That documentary series about the climate is simple, but still interesting to watch at night.

Serial dokumenter means a documentary series (multiple episodes under one title).
Serial here is a borrowed word from English, but in Indonesian it specifically suggests:

more than one episode
usually shown on TV or streaming platforms

Film dokumenter is a documentary film — normally a single, self‑contained movie.

So:

serial dokumenter = a series of episodes
film dokumenter = one documentary film

Both are natural; you choose based on whether it’s episodic or a single film.

Why is it serial dokumenter tentang iklim itu and not serial dokumenter itu tentang iklim? How does word order work here?

Both are grammatical, but the nuance is different.

Serial dokumenter tentang iklim itu …
Literally: that documentary series about climate …
- tentang iklim directly modifies serial dokumenter (it tells you what kind of series)
- itu at the end points to a specific one both speaker and listener know
Serial dokumenter itu tentang iklim.
Literally: That documentary series is about climate.
- Here tentang iklim is more like new information, an explanation of what it is about
- It sounds more like a full statement: That series is about climate.

In your sentence, the speaker is already treating it as “that climate documentary series we know about”, so tentang iklim is inside the noun phrase, and itu comes at the end of that phrase.

What is the function of itu here? Why is it after iklim instead of before, like itu serial dokumenter?

Indonesian commonly places itu after the noun (or entire noun phrase) to mean “that specific …”.

serial dokumenter itu = that (particular) documentary series
serial dokumenter tentang iklim itu = that (particular) documentary series about climate

Compare these:

itu serial dokumenter – possible, but sounds more like pointing: that’s a documentary series (deictic, like that over there).
serial dokumenter itu – the documentary series we’ve been talking about (definite, known from context).

In your sentence, itu makes the series definite and known: that climate documentary series (we already know about).

Why is sederhana placed after the noun instead of before it? I thought adjectives follow nouns in Indonesian.

In this sentence, sederhana is not describing the noun directly; it’s part of the predicate:

Serial dokumenter … itu sederhana, tapi tetap menarik …

Here the structure is:

[subject]: Serial dokumenter tentang iklim itu
[predicate]: sederhana, tapi tetap menarik untuk ditonton malam hari.

So sederhana means is simple (the series is simple).

If you wanted an adjective directly modifying the noun, you’d do:

serial dokumenter yang sederhana = a simple documentary series (as an attribute)

So:

After the noun as predicate: Serial itu sederhana. (The series is simple.)
After the noun as attribute: serial yang sederhana (a simple series).

What’s the difference between tapi and tetapi? Is tapi informal here?

Tapi and tetapi both mean “but/however”, and grammatically they work the same way.

tapi – more colloquial and frequent in everyday speech and informal writing
tetapi – a bit more formal or neutral, common in essays, news, formal writing

Your sentence with tetapi is also correct:

Serial dokumenter tentang iklim itu sederhana, tetapi tetap menarik untuk ditonton malam hari.

In casual conversation or subtitles, tapi is very natural.

What does tetap add to the meaning in tapi tetap menarik? Could we just say tapi menarik?

Tetap literally means “still / remains / stays”.

tapi menarik = but (it is) interesting
tapi tetap menarik = but (it is) still / nevertheless interesting

Tetap emphasizes that even though it’s simple, it does not stop being interesting. It signals a contrast:

Expectation: simple → maybe boring
Reality: simple, yet still interesting

Without tetap, it’s a weaker contrast; with tetap, the “despite that, it’s still interesting” nuance is stronger.

How does untuk ditonton work grammatically? Why ditonton (passive) and not menonton (active)?

Untuk ditonton literally means “to be watched”.

Breakdown:

untuk = for / in order to / to
ditonton = passive form of menonton (to watch), so to be watched

Patterns:

untuk + active verb (meN-) = for someone to do something
- untuk menonton = to watch (for someone to watch)
untuk + passive verb (di-) = for something to be done to it
- untuk ditonton = to be watched

Here, menarik untuk ditonton = interesting to watch
You are describing the series as something that is interesting for people to watch.

If you said menarik untuk menonton, it sounds more like interesting for (someone) to do the act of watching — less idiomatic in this context. With things like movies, shows, books, the common pattern is:

menarik untuk dibaca – interesting to read
menarik untuk ditonton – interesting to watch
enak untuk dimakan – tasty to eat (lit. tasty to be eaten)

Is ditonton here referring to “by me”, “by us”, or “by people in general”? There is no explicit subject.

In Indonesian passive forms like ditonton, if there’s no agent mentioned, it usually means “(to be) watched by people (in general)” or “by whoever”.

So menarik untuk ditonton means:

interesting to watch (for people in general)
equivalent to English adjectives like watchable, fun to watch

You don’t need to specify oleh saya / oleh kita etc.; it’s understood from context that it’s about viewers, such as the speaker and listener.

What does malam hari mean exactly, and how is it different from just malam or pada malam hari?

All three are related and all can be correct:

malam = night / evening
malam hari = literally night time, often a bit more explicit or emphasized
pada malam hari = at night (with the preposition pada “at/on”)

In your sentence:

menarik untuk ditonton malam hari
= interesting to watch at night / in the evening

Subtle differences:

malam – shortest and most casual
malam hari – slightly more “complete”; often used in neutral or semi-formal speech and writing
pada malam hari – sounds more formal or very explicit about the time

You could also say:

…menarik untuk ditonton malam-malam. – more casual, “at night / late at night” with a relaxed tone.

Can any words be safely omitted without changing the meaning too much? For example, can I drop itu, hari, or tetap?

Yes, you can omit some elements depending on the nuance you want:

Dropping itu
- Serial dokumenter tentang iklim sederhana, tapi tetap menarik untuk ditonton malam hari.
  Still understandable, but it now sounds more like “a climate documentary series (in general)”, not “that specific one we both know”.
Dropping hari
- …menarik untuk ditonton malam.
  This is still okay and common in speech. Malam alone already implies at night / in the evening. Malam hari is just a bit fuller.
Dropping tetap
- …sederhana, tapi menarik untuk ditonton malam hari.
  Grammatically fine, but you lose the “even though it’s simple, it’s still interesting” emphasis. It becomes a milder contrast.

So:

itu – controls specific vs. general reference
hari – stylistic; malam alone is often enough
tetap – adds the “despite that, still …” contrast and sounds more expressive