Learn Hardcore Indonesian: Di komunitas itu, ada yang mengajar anak kecil, ada yang melatih keterampilan berbicara. - In that community, some teach small children, some train speaking skills.

Ada literally means there is / there are.
Yang is a marker that introduces a clause describing something, often translated as that / who / which.

In this sentence:

Ada yang mengajar anak kecil
≈ There are (people) who teach small children.

So ada yang together often means “there is/are someone/people who …” or “some (people) …”. It’s a very common pattern:

Ada yang suka membaca, ada yang suka menulis.
Some (people) like reading, some (people) like writing.

What is the function of yang in ada yang mengajar anak kecil and ada yang melatih keterampilan berbicara?

Yang turns what follows into a descriptive clause, like who/that + verb in English.

yang mengajar anak kecil → who teach small children
yang melatih keterampilan berbicara → who train speaking skills

In ada yang mengajar…, the noun (orang = person/people) is understood but not spoken:

Ada orang yang mengajar anak kecil.
There are people who teach small children.

Native speakers often drop orang and just say ada yang…, because it’s clear from context that we’re talking about people.

Who is the subject in these clauses? There is no word like people in the sentence.

The subject is implicit. Grammatically, you can think of it as:

[Ada orang] yang mengajar anak kecil
[Ada orang] yang melatih keterampilan berbicara

where orang (people) is omitted.

Indonesian often omits things that are obvious from context. In this structure, listeners automatically understand that yang … refers to people:

Ada yang datang terlambat.
Some (people) came late.

You could add orang if you want to be very explicit:

Di komunitas itu, ada orang yang mengajar anak kecil…
But in everyday speech, ada yang… is more natural.

Could I say Di komunitas itu, orang-orang mengajar anak kecil dan melatih keterampilan berbicara instead? What’s the difference in nuance?

You can say:

Di komunitas itu, orang-orang mengajar anak kecil dan melatih keterampilan berbicara.

This means roughly:

In that community, people teach small children and train speaking skills.

But the nuance is different:

Ada yang … ada yang …
emphasizes different groups doing different activities:
Some people do X, and some people do Y (and maybe they’re not the same people).
Orang-orang mengajar … dan melatih …
implies one group of people who do both activities, or at least doesn’t highlight the distinction.

The original sentence explicitly contrasts two groups:
some teach children, some train speaking skills.

Why is there a comma instead of dan before ada yang melatih…? Can I use dan?

Yes, you can say:

Di komunitas itu, ada yang mengajar anak kecil dan ada yang melatih keterampilan berbicara.

The meaning is basically the same.

Using just a comma:

…, ada yang mengajar…, ada yang melatih…

is a common stylistic choice in Indonesian, especially in writing or formal speech, to present a list of contrasting or parallel clauses.

So:

With dan: a little more “joined together” grammatically.
With only commas: feels a bit more like listing or emphasizing the contrast: one group does this, another does that.

What does di komunitas itu imply? How is it different from just di komunitas?

Di komunitas itu means in that community (a specific one already known in the conversation).

di = in/at
komunitas = community
itu = that (marks something as specific/previously mentioned)

If you say just di komunitas, it feels incomplete, like saying “in community” without specifying which one. You would usually add something:

di komunitas kami (in our community)
di komunitas online (in the online community)

So itu here is like English the/that: it points to a particular community that both speaker and listener know.

Is anak kecil singular or plural here? Why not anak-anak kecil?

Anak kecil literally: small child
But in context, it can mean small children / little kids in general.

Indonesian often leaves number (singular/plural) unspecified unless it needs to be clear. So:

mengajar anak kecil = teaching small child(ren) / teaching little kids

If you want to emphasize plurality, you could say:

mengajar anak-anak kecil
(literally “small children-children” → clearly plural)

In everyday speech, anak kecil is very commonly used to mean little kids as a group, so the original sentence is natural and doesn’t sound singular.

What is the difference between mengajar and melatih in this sentence?

Mengajar = to teach, usually about knowledge or school-type learning.
Here: mengajar anak kecil = teaching small children (school subjects, basic literacy, etc.)
Melatih = to train / to coach, usually about skills or practice.
Here: melatih keterampilan berbicara = training/practising speaking skills.

So the sentence suggests two types of activities:

More general/academic teaching for kids (mengajar)
Skill-focused training in speaking (melatih)

What exactly does keterampilan berbicara mean, and how is it formed?

Keterampilan berbicara = speaking skills.

Breakdown:

terampil = skilled
ke-…-an = a noun-forming prefix–suffix pair
keterampilan ≈ skill(s) / proficiency
berbicara = to speak

So:

keterampilan berbicara = skill(s) of speaking → speaking skill(s)

You could also hear:

kemampuan berbicara (ability to speak)
melatih berbicara (training speaking) without the noun keterampilan

But melatih keterampilan berbicara is a natural, slightly more formal way to say train/develop speaking skills.

What tense is this sentence? How do we know whether it’s present, past, or future?

Indonesian verbs don’t change form for tense. Mengajar and melatih stay the same for past, present, or future.

The tense is usually inferred from context. This sentence could be translated as:

In that community, some (people) teach small children, some train speaking skills. (general/habitual)
In that community, there were some who taught small children, some who trained speaking skills. (past, if the surrounding context is past)

If you want to make the time clearer, you add time words:

Dulu, di komunitas itu, ada yang mengajar anak kecil… (In the past…)
Sekarang, di komunitas itu, ada yang mengajar anak kecil… (Now…)
Nanti, di komunitas itu, akan ada yang mengajar… (Later, there will be some who teach…)

Is this sentence formal, informal, or neutral? In what situations could I use it?

The sentence is neutral and quite natural. You can use it:

in everyday conversation
in semi-formal presentations
in written descriptions (e.g. explaining what a community does)

Nothing in the sentence is slangy or overly formal. Words like komunitas, keterampilan, and this ada yang… ada yang… pattern are common in both spoken and written Indonesian.

Can I move di komunitas itu to the end and say Ada yang mengajar anak kecil, ada yang melatih keterampilan berbicara di komunitas itu?

You can, but the nuance shifts slightly.

Di komunitas itu, ada yang… ada yang…
→ Emphasizes the community first: In that community, there are some who do X and some who do Y.
Ada yang mengajar anak kecil, ada yang melatih keterampilan berbicara di komunitas itu.
→ Sounds more like you’re adding “in that community” only to the second clause, or as an afterthought.

If you want to keep it clearly modifying both clauses, the original word order is better and more natural:

Di komunitas itu, ada yang mengajar anak kecil, ada yang melatih keterampilan berbicara.