Learn Hardcore Indonesian: Kelas teaterku diadakan setiap Rabu malam, sedangkan latihan musik adik laki-lakiku hari Kamis pagi. - My theater class is held every Wednesday night, while my younger brother’s music practice is on Thursday morning.

-ku is:
- more informal / neutral
- very common in speech and writing
- attached directly to the noun: buku → bukuku (my book)
saya is:
- more formal and polite
- usually written as a separate word: kelas teater saya

So kelas teaterku sounds a bit more casual or neutral; kelas teater saya sounds more formal or careful. Both are correct.

Why is diadakan used in kelas teaterku diadakan setiap Rabu malam? What does it add?

Diadakan is a passive verb meaning is held / is organized / takes place.

Root: ada (to exist / there is)
Verb: mengadakan (to hold/organize something, e.g. mengadakan rapat = to hold a meeting)
Passive: diadakan (to be held)

So kelas teaterku diadakan setiap Rabu malam literally =
my theater class is held every Wednesday evening.

You could also say:

Kelas teaterku ada setiap Rabu malam.
(My theater class exists / is on every Wednesday night.)

Using diadakan makes it sound more like an organized event rather than just something that exists. It’s natural for scheduled events like classes, meetings, workshops, etc.

Could you drop diadakan and just say Kelas teaterku setiap Rabu malam?

You can, but then the sentence feels incomplete on its own.

In informal speech, people might say something like:

Kelas teaterku setiap Rabu malam, latihan musik adik laki-lakiku hari Kamis pagi.

Listeners will understand that is held / takes place is implied, but grammatically a verb is missing in the first clause.

For clear, neutral Indonesian, it is better to keep diadakan (or another verb like ada or berlangsung) in the first clause:

Kelas teaterku diadakan setiap Rabu malam.
Kelas teaterku ada setiap Rabu malam.

Why is there no verb like diadakan or ada in the second part: latihan musik adik laki-lakiku hari Kamis pagi?

This is an example of ellipsis and parallel structure.

The full, explicit version would be:

Kelas teaterku diadakan setiap Rabu malam, sedangkan latihan musik adik laki-lakiku diadakan hari Kamis pagi.

In the second clause, diadakan is understood from context, so it is omitted to avoid repetition. This is very common in Indonesian when two clauses share the same verb:

Saya makan nasi, dia (makan) mie.
Dia beli buku, saya (beli) pensil.

So you can mentally read it as:

latihan musik adik laki-lakiku (diadakan) hari Kamis pagi.
= my younger brother’s music practice is (held) on Thursday morning.

What is the role of sedangkan here? How is it different from just dan or from sementara?

Sedangkan connects two clauses and shows contrast or difference, similar to while / whereas in English.

Kelas teaterku diadakan setiap Rabu malam, sedangkan latihan musik adik laki-lakiku hari Kamis pagi.
≈ My theater class is held every Wednesday evening, while/whereas my younger brother’s music practice is on Thursday morning.

Differences:

dan = and, neutral, just adds things:
- Kelas teaterku diadakan setiap Rabu malam dan latihan musik adik laki-lakiku hari Kamis pagi.
  (Correct, but the contrast in day/time is weaker.)
sementara often also means while, and can be similar to sedangkan, but:
- sedangkan is more explicitly contrastive: A is like this, whereas B is like that.
- sementara can mean during the time that or for the time being depending on context.

Here, sedangkan is a good choice because you are contrasting your schedule with your brother’s schedule.

What exactly does adik laki-laki mean? Why is laki-laki repeated?

Adik laki-laki means younger brother (younger male sibling).

Breakdown:

adik = younger sibling (gender not specified)
laki-laki = male, man

So adik laki-laki = younger sibling who is male → younger brother.

The repetition in laki-laki is reduplication. The base word laki is not really used on its own; laki-laki as a fixed phrase means male or man. You don’t say adik laki; you must use adik laki-laki.

Why is the possessive -ku attached to laki-laki and not to adik in adik laki-lakiku?

In practice, adik laki-lakiku is understood as my younger brother as a whole unit.

Formally, the possessive suffix -ku is attached to the last noun in the noun phrase:

adik laki-laki (younger brother)
adik laki-lakiku (my younger brother)

It doesn’t mean my male, it still means my younger brother; possession applies to the entire phrase.

Other examples:

rumah sakit (hospital) → rumah sakitku (my hospital / the hospital I go to)
guru matematika (math teacher) → guru matematikaku (my math teacher)

Grammatically, Indonesian typically puts the possessive marker on the last noun in the phrase.

Could you say adik laki-laki saya instead of adik laki-lakiku? Is there any difference?

Yes, you can say adik laki-laki saya, and it is completely correct.

Comparison:

adik laki-lakiku = younger brother (my), with suffix -ku attached; slightly more informal/neutral.
adik laki-laki saya = younger brother (I), using saya; more formal/polite.

Meaning is the same. Choice depends on the level of formality and personal style.

Why is setiap used before Rabu malam? What does it do, and could it go in a different place?

Setiap means every / each.

setiap Rabu malam = every Wednesday evening

Position:

setiap goes directly before the time noun:
- setiap hari = every day
- setiap pagi = every morning
- setiap bulan = every month
- setiap Rabu malam = every Wednesday night

You can’t move it to another place like in English (Wednesday every night). In Indonesian, the natural position is setiap + time word:

Kelas teaterku diadakan setiap Rabu malam.
You could also say Kelas teaterku diadakan setiap malam Rabu, but that sounds older/less common in modern standard usage.

Why is it Rabu malam and Kamis pagi, and not malam Rabu or pagi Kamis?

Typical word order for day and part of day is:

[day] [part of day]

So you say:

Senin pagi (Monday morning)
Selasa malam (Tuesday night)
Rabu malam (Wednesday evening/night)
Kamis pagi (Thursday morning)

Malam Rabu and pagi Kamis do exist, but they are less common in everyday modern speech and can sound more old-fashioned or regional. For learners, day + part of day is the safest and most natural pattern.

Why is hari included before Kamis pagi but not before Rabu malam?

Both Rabu and hari Rabu are correct.

You have options:

setiap Rabu malam
setiap hari Rabu malam
hari Kamis pagi
Kamis pagi

People often omit hari (day) when the meaning is clear. In your sentence:

setiap Rabu malam: hari is omitted for brevity.
hari Kamis pagi: hari is included, but it could also be omitted without changing the meaning.

So you could also say:

Kelas teaterku diadakan setiap hari Rabu malam, sedangkan latihan musik adik laki-lakiku Kamis pagi.
Kelas teaterku diadakan setiap Rabu malam, sedangkan latihan musik adik laki-lakiku Kamis pagi.

All are acceptable; differences are very minor, mostly style/rhythm.

Is a preposition like pada needed before the time expressions (e.g., pada setiap Rabu malam)?

You can add pada, but it’s not required.

All of these are grammatically fine:

Kelas teaterku diadakan setiap Rabu malam.
Kelas teaterku diadakan pada setiap Rabu malam.
Kelas teaterku diadakan pada Rabu malam.

In natural, everyday Indonesian:

pada is often omitted, especially with clear time expressions.
Including pada can make the sentence sound a bit more formal or written.

So diadakan setiap Rabu malam (without pada) is perfectly normal.

Are the days of the week like Rabu and Kamis always capitalized?

In standard Indonesian writing (especially in formal contexts), days of the week are capitalized:

Senin, Selasa, Rabu, Kamis, Jumat, Sabtu, Minggu

So Rabu and Kamis are correctly capitalized in the sentence.

In very informal writing (e.g. chats, texts), you may see them in lowercase, but for correct standard Indonesian, use capital letters.