Learn Hardcore Indonesian: Di perpustakaan, saya menandai beberapa kata sulit dengan stabilo, supaya nanti saya cukup membuka halaman itu lagi. - In the library, I mark some difficult words with a highlighter, so later I just need to open that page again.

Di perpustakaan, saya menandai...
Literally: In the library, I marked...
This puts extra emphasis on the place (the library). It’s like setting the scene: As for what happens in the library…
Saya menandai beberapa kata sulit dengan stabilo di perpustakaan...
This feels more neutral: subject (saya) first, then the action and location.

Both are grammatically correct. In Indonesian, it’s very natural to put a place expression like di perpustakaan at the beginning to provide context, similar to “At the library, I…” in English.

What is the role of di in di perpustakaan? Is it the same di as the passive prefix?

No, these are two different di’s:

In di perpustakaan, di is a preposition meaning in/at/on (location).
- di rumah = at home
- di sekolah = at school
The di- that marks passive voice is a prefix attached to a verb:
- tulis → ditulis (is/was written)
- buat → dibuat (is/was made)

You can tell di is a preposition here because:

It stands alone as a word.
It’s followed by a noun (perpustakaan, library), not a verb.

What does menandai mean exactly, and how is it formed?

Menandai means to mark or to put a mark on something.

It’s formed from the noun tanda (mark, sign) with the me-…-i verb pattern:

tanda → menandai
- Literally “to give a mark to [something]”
- It’s a transitive verb: you menandai something.

Example:

Saya menandai kata-kata penting.
I mark the important words.

There’s also menandakan, which usually means to signify / to indicate (more abstract):

Ini menandakan awal yang baru.
This signifies a new beginning.

In your sentence, menandai (to physically mark words with a highlighter) is the correct choice.

Why is it beberapa kata sulit and not beberapa kata-kata sulit?

In Indonesian, you normally do not combine:

a plural marker like beberapa (some/several)
with
the reduplicated plural form kata-kata

You choose one way to show plurality:

beberapa kata sulit = some difficult words
kata-kata sulit = difficult words (in general, plural by context)

Beberapa kata-kata sulit is considered redundant and unnatural in standard Indonesian.

Does kata sulit here mean one difficult word or difficult words?

In this sentence, kata sulit is plural in meaning: difficult words.

Plurality in Indonesian is often shown by:

context, or
words like beberapa, banyak, semua, etc.

Since we have beberapa (some/several), the phrase beberapa kata sulit clearly refers to more than one difficult word, even though kata itself is not reduplicated.

Could I say beberapa kata yang sulit instead of beberapa kata sulit? What’s the difference?

Yes, you can say both:

beberapa kata sulit
beberapa kata yang sulit

Both mean some difficult words and are correct.

Nuances (very slight):

kata sulit = noun + adjective directly; common and a bit more compact.
kata yang sulit = noun + relative clause; can sound a tiny bit more descriptive or explicit: words that are difficult.

In normal conversation and writing, beberapa kata sulit is perfectly natural and slightly simpler.

What is stabilo in dengan stabilo? Why not say penyorot or something like that?

Stabilo is actually a brand name (like “Stabilo Boss”), but in everyday Indonesian it’s widely used as a generic word for a highlighter pen.

So dengan stabilo means with a highlighter.

More “generic” or formal options would be:

dengan pena penyorot (with a highlighter pen)
dengan spidol penanda (with a marker)

But in real-life speech, people very often just say stabilo, regardless of the actual brand, similar to saying “a Kleenex” in English for any tissue.

Why is it dengan stabilo? Could I say pakai stabilo instead?

Yes, both are correct and common:

dengan stabilo = with a highlighter
pakai stabilo = using a highlighter

Nuance:

dengan is a bit more neutral or formal.
pakai is casual, very common in spoken Indonesian.

In a written or neutral context, dengan stabilo works very well, as in your sentence.

What does supaya do in this sentence? How is it different from agar, biar, or untuk?

Supaya introduces a purpose or desired result, similar to “so that / in order that” in English.

In the sentence:

..., supaya nanti saya cukup membuka halaman itu lagi.
= ..., so that later I only need to open that page again.

Comparisons:

supaya: neutral, standard, very common in writing and speech.
agar: slightly more formal/literary than supaya, but same meaning.
biar: more informal/colloquial; same basic meaning.
untuk: usually “for / to” (indicating purpose) but grammatically different:
- Saya menandai beberapa kata sulit untuk belajar nanti.
  I marked some difficult words to study later.
  Here it links to a verb phrase (belajar), not a full clause with a subject.

In your sentence, supaya is ideal: it links to a full clause (nanti saya cukup membuka...).

How is nanti being used here? Does it mean “in the future” in general?

Nanti means later, usually later on / at some point after this, not distant future.

In your sentence:

supaya nanti saya cukup membuka halaman itu lagi
= so that later I only need to open that page again

It implies:

Not right now, but at a later time when I return to this book or these notes.

Other examples:

Nanti malam saya belajar. = I’ll study tonight.
Bisa kita bicara nanti? = Can we talk later?

It doesn’t usually mean vague long-term future like “in ten years”; it’s more short- to medium-term, depending on context.

What does cukup mean in saya cukup membuka halaman itu lagi?

Here cukup means “only need to / just have to”, not “enough” in the usual quantitative sense.

saya cukup membuka halaman itu lagi
≈ I just need to open that page again
≈ It’s enough if I just open that page again

Other similar uses:

Kamu cukup belajar satu jam.
You only need to study for one hour / One hour is enough for you to study.
Saya cukup bilang sekali.
I just need to say it once.

So in this pattern cukup + verb, it expresses that that action alone is sufficient.

Why halaman itu and not just halaman? What does itu add?

Itu is a demonstrative meaning that. Here it points to a specific page, the one that was marked earlier.

halaman = (a) page (in general, not specified)
halaman itu = that specific page (the previously mentioned one)

So:

membuka halaman itu lagi = to open that (already known) page again

If you said just membuka halaman lagi, it would mean “open more pages again / open pages again”, and sounds vague or even like “another page”, not “the same marked page”.

Could I move lagi earlier and say membuka lagi halaman itu?

Yes, membuka lagi halaman itu is also grammatically correct and understandable.

Word order nuances:

membuka halaman itu lagi
Very commonly used; feels smooth and natural.
Literally: “open that page again.”
membuka lagi halaman itu
Also okay, but lagi usually comes after the verb or at the end, so many speakers prefer the first version.

In practice, membuka halaman itu lagi is the more typical phrasing.

How formal or informal is the whole sentence? Could I use aku or biar instead?

The sentence as given is neutral to slightly formal, but still natural in everyday use:

saya = neutral / polite first-person pronoun
supaya = neutral, standard
dengan = neutral

More informal version:

Di perpustakaan, aku menandai beberapa kata sulit pakai stabilo, biar nanti aku cuma buka halaman itu lagi.

Changes:

aku instead of saya (more intimate, casual)
pakai instead of dengan (colloquial)
biar instead of supaya (informal)
cuma instead of cukup (very common colloquial equivalent in this sense)

Your original sentence is appropriate for written work, narration, or polite conversation.