Learn Hardcore Indonesian: Orang dewasa juga belajar di perpustakaan malam ini. - Adults also study in the library tonight.

A / one adult:
- seorang dewasa (literally “one person [who is] adult”)
- satu orang dewasa (more explicitly “one adult person”)
Several adults / adults (plural):
- orang-orang dewasa (reduplication marks plural, sounds a bit formal or emphatic)
- para orang dewasa (“the adults” as a group, quite formal / written style)

So your sentence could become:

Seorang dewasa juga belajar di perpustakaan malam ini. – One adult …
Para orang dewasa juga belajar di perpustakaan malam ini. – The adults (as a group) …

Why is there no word for “the” or “a” before orang dewasa or perpustakaan?

Indonesian does not use articles like “a/an” or “the”. Nouns appear without them, and context tells you whether you mean “a”, “the”, or just “(some)”.

So:

orang dewasa can be “an adult”, “the adult”, or “adults”.
perpustakaan can be “a library” or “the library”.

If you really need to be specific, you use other words:

satu / seorang for “one/a”
itu for “that / the (specific)”
- perpustakaan itu – that library / the library (that we both know about)

What exactly does juga mean here, and where can it go in the sentence?

juga means “also / too / as well”.

In your sentence, juga comes after the subject:

Orang dewasa juga belajar… – Adults also study…

The most natural positions are:

After the subject: Orang dewasa juga belajar di perpustakaan malam ini.
After another element you want to emphasize:
- Orang dewasa belajar juga di perpustakaan malam ini. (can sound like “they do study, too”, but less common)
- Orang dewasa belajar di perpustakaan juga malam ini. (awkward; native speakers rarely place it like this)

For standard, natural Indonesian, put juga right after the subject or right before the verb phrase, as in the original sentence.

How do I know the tense of belajar here? Is it “study”, “are studying”, or “will study”?

Indonesian verbs like belajar don’t change form for tense. The time is understood from context and time words.

With malam ini (“tonight / this evening”), your sentence can be understood as:

“Adults are studying at the library tonight.” (plan / arrangement)
“Adults will study at the library tonight.”

To be more explicit:

sedang belajar – “are studying (right now / in progress)”
akan belajar – “will study”

Examples:

Orang dewasa sedang belajar di perpustakaan malam ini. – Adults are studying at the library tonight (focus on ongoing activity).
Orang dewasa akan belajar di perpustakaan malam ini. – Adults will study at the library tonight (future plan).

What is the difference between malam ini and nanti malam?

Both relate to “tonight”, but there’s a nuance:

malam ini – literally “this night”; neutral “tonight” (today’s night).
nanti malam – literally “later tonight”; often used when it’s still daytime and you mean “later this evening”.

Many speakers use them almost interchangeably, but:

At noon/afternoon, both malam ini and nanti malam are natural.
Right before the activity, malam ini may sound slightly more neutral, while nanti malam still emphasizes “later”.

Your sentence with either:

Orang dewasa juga belajar di perpustakaan malam ini. – Adults also study at the library tonight.
Orang dewasa juga belajar di perpustakaan nanti malam. – Adults also study at the library later tonight.

Why is it di perpustakaan and not ke perpustakaan?

Indonesian distinguishes between location and movement:

di = “at / in / on” (location, where something is)
- di perpustakaan – at the library
ke = “to” (movement toward a place)
- ke perpustakaan – to the library

In your sentence, the focus is on where they are studying:

belajar di perpustakaan – studying at the library.

If you talk about going there, you’d use:

Orang dewasa juga pergi ke perpustakaan malam ini. – Adults are also going to the library tonight.

Can I move malam ini to the beginning or another part of the sentence?

Yes. Time expressions are flexible in Indonesian. All of these are grammatical:

Orang dewasa juga belajar di perpustakaan malam ini. (original; very natural)
Malam ini, orang dewasa juga belajar di perpustakaan.
Orang dewasa malam ini juga belajar di perpustakaan. (understandable, but less common; sounds a bit heavy in the middle)

Most natural options are:

[Subject] + [adverb] + [verb] + [place] + [time]
- Orang dewasa juga belajar di perpustakaan malam ini.
[Time] + [subject] + [adverb] + [verb] + [place]
- Malam ini orang dewasa juga belajar di perpustakaan.

Putting malam ini at the very start is common and sounds natural, especially in spoken or narrative style.

Is belajar “to learn” or “to study”? Could it mean “teach”?

belajar means “to study / to learn” (from the learner’s perspective), not “to teach”.

belajar – to study / to learn
- Saya belajar di perpustakaan. – I study / I’m studying at the library.
mengajar – to teach
- Dia mengajar di perpustakaan. – He/She teaches at the library.

So in your sentence, the adults are the ones studying/learning, not teaching:

Orang dewasa juga belajar di perpustakaan malam ini. – Adults are also studying/learning at the library tonight.

Can I say just dewasa instead of orang dewasa?

In this kind of sentence, you normally need the word orang.

orang dewasa – literally “adult person”; means “adult(s)” (as a noun)
dewasa on its own is usually an adjective – “adult / mature”

For example:

Dia sudah dewasa. – He/She is already an adult / mature. (adjective)
Orang dewasa juga belajar di perpustakaan malam ini. – Adults also study… (noun phrase)

If you try:

Dewasa juga belajar di perpustakaan malam ini. – sounds wrong/unnatural as a standalone subject.

To talk about “the adults” as people, use orang dewasa (or para orang dewasa in formal style).

Is there a way to say clearly “the adults” (specific group) instead of just “adults in general”?

Yes. You can make the group more specific using itu or para:

orang dewasa itu – that adult / those adults
- Orang dewasa itu juga belajar di perpustakaan malam ini.
  – That adult / Those adults also study at the library tonight.
para orang dewasa – the adults (as a group, formal)
- Para orang dewasa juga belajar di perpustakaan malam ini.

para is typically used in more formal or written Indonesian (announcements, articles, etc.). In everyday speech, orang dewasa itu or just orang dewasa plus context is more common.

If I want to say “are also studying right now at the library tonight”, do I need sedang as well?

You can add sedang to emphasize the ongoing nature of the action (similar to English “am/is/are -ing”).

Some options:

Orang dewasa juga sedang belajar di perpustakaan malam ini.
– Adults are also (currently) studying at the library tonight.
Orang dewasa malam ini juga sedang belajar di perpustakaan. (less common order, but grammatical)

Notes:

sedang often refers to something happening around now. Adding malam ini can sound like either “they are in the middle of that study session this evening” or “they will be in that state this evening” (depending on context).
In many everyday situations, sedang is optional; context and time words already explain enough.

Could I replace di perpustakaan with a pronoun like “there”? How would that work?

Yes. You can use di sana (“there”) to avoid repeating perpustakaan when it’s already clear from context.

For example, if someone already mentioned the library:

Orang dewasa juga belajar di sana malam ini.
– Adults also study there tonight.

Breakdown:

di perpustakaan – at the library
di sana – there (at that place)

Indonesian doesn’t use a direct equivalent of English “there” as a subject placeholder (“There are adults…”), but di sana works well as a place pronoun.