Learn Hardcore Indonesian: Musisi dan desainer berbagi portofolio mereka di konser kecil setiap musim panas. - Musicians and designers share their portfolios at a small concert every summer.

In this sentence, mereka (“they / their”) shows that the speaker is thinking of more than one person, so the natural English is “Musicians and designers share their portfolios …”.

If you want to make plural very clear, you can say:

para musisi dan desainer = (all / several) musicians and designers
musisi dan desainer-desainer = musicians and (several) designers (less natural here, and a bit clunky)

Why is mereka used instead of dia? What does mereka refer to here?

dia = he / she (singular)
mereka = they / them / their (plural)

In Musisi dan desainer berbagi portofolio mereka …, mereka refers back to musisi dan desainer. Because we are talking about more than one person, we must use mereka, not dia.

So:

Musisi itu berbagi portofolionya. = The musician shares his/her portfolio.
Musisi dan desainer berbagi portofolio mereka. = Musicians and designers share their portfolios.

What exactly does berbagi mean, and how is it different from membagikan?

berbagi is an intransitive verb meaning “to share (something)”, often focusing on the action of sharing in general.

berbagi portofolio = share portfolios
berbagi cerita = share stories
berbagi makanan = share food

membagikan is more like “to distribute / to hand out” something to others and is more clearly transitive.

membagikan portofolio kepada penonton = distribute / hand out portfolios to the audience
membagikan selebaran = hand out flyers

In this sentence, berbagi portofolio is natural because the idea is that they are sharing or presenting their portfolios, not physically handing many copies out.

Does portofolio mean “portfolio” or “portfolios”? How do you show singular vs plural?

Portofolio is a loanword from English portfolio and can be singular or plural, depending on context. Indonesian usually doesn’t change the word form for plural.

portofolio = (a) portfolio / portfolios
portofolio mereka = their portfolio(s)

In this sentence, Musisi dan desainer berbagi portofolio mereka is best understood as “share their portfolios”, because there are multiple people and each likely has their own portfolio.

To make a plural very explicit, you can say portofolio-portofolio, but this is often unnecessary and can sound heavy in casual speech.

Why is it konser kecil and not kecil konser? Where do adjectives go?

In Indonesian, adjectives normally come after the noun they describe:

konser kecil = small concert
rumah besar = big house
kota tua = old city

So konser kecil is correct. kecil konser would be wrong in standard Indonesian.

If you want to add more adjectives, you keep them after the noun:

konser kecil tahunan = small annual concert
konser kecil dan intim = small and intimate concert

What’s the difference between di konser kecil and ke konser kecil? Why is di used here?

di = at / in / on (location)
ke = to / towards (movement, direction)

In di konser kecil, di shows location: at the small concert.

If you said ke konser kecil, it would mean “to the small concert,” focusing on movement/going there:

Mereka pergi ke konser kecil. = They go to the small concert.
Mereka tampil di konser kecil. = They perform at the small concert.

Here, because the action (sharing portfolios) happens at the concert, di konser kecil is correct.

Could we use pada instead of di in di konser kecil? What’s the nuance?

In this sentence:

di konser kecil = at the small concert
pada konser kecil = at the small concert (more formal / written)

di is the normal, everyday preposition for physical location.
pada is common in formal writing and is also used with time expressions and abstract “locations”:

pada tahun 2020 = in 2020
pada kesempatan ini = on this occasion
pada konser kecil ini (very formal) = at this small concert

So di konser kecil sounds more natural in ordinary speech and neutral writing.

What does setiap musim panas mean exactly? Is it like “every summer” or “each summer”?

setiap means every / each.
musim panas = summer (literally “hot season”).

So setiap musim panas = every summer / each summer.

You can also say:

tiap musim panas = every summer (more casual)
setiap tahun = every year
setiap hari = every day

Is musim panas a natural phrase in Indonesian, since Indonesia is tropical?

In everyday Indonesian, people more often talk about:

musim hujan = rainy season
musim kemarau = dry season

However, musim panas is understood and used, especially:

in school contexts (explaining four seasons)
when talking about countries with four seasons
in translated materials, songs, etc.

So setiap musim panas is grammatically correct and understandable, but in a local Indonesian context you might more naturally hear something like setiap musim kemarau depending on the meaning.

There’s no tense marker in berbagi. How do I know if it means “share”, “shared”, or “will share”?

Indonesian verbs usually don’t change for tense. berbagi can mean:

share (present / habitual)
shared (past)
will share (future)

The time is understood from context or from time words:

Musisi dan desainer berbagi portofolio mereka di konser kecil setiap musim panas.
→ By default, this is a habitual action: “(They) share … every summer.”

To make tense more explicit:

Sudah berbagi = have already shared (past / completed)
Tadi berbagi = just now shared
Akan berbagi = will share (future)

Example:

Mereka akan berbagi portofolio mereka di konser kecil besok.
= They will share their portfolios at a small concert tomorrow.

Is there any verb change for plural subjects in Indonesian? Should berbagi change because the subject is plural?

No. Indonesian verbs do not change based on the number or person of the subject.
berbagi stays berbagi for:

Saya berbagi = I share
Dia berbagi = He/She shares
Mereka berbagi = They share
Musisi dan desainer berbagi = Musicians and designers share

So you never add endings like -s or change the verb form the way English does.

Could you say Musisi dan para desainer or Para musisi dan desainer? What’s the difference?

Yes:

Musisi dan desainer
= musicians and designers (number not strongly emphasized)
Musisi dan para desainer
= the musician(s) and the designers (with para emphasizing that desainer are plural)
Para musisi dan desainer
= (all / many) musicians and designers (now musisi is clearly plural; desainer is understood as plural by parallelism)

para is used before nouns for groups of people and adds a sense of “(all) the …” or “a group of …”:

para guru = the teachers
para seniman = the artists

In everyday speech, Musisi dan desainer is already fine; para just makes the plural more explicit or slightly more formal.

Could we say Portofolio mereka dibagikan di konser kecil … instead? What’s the difference in meaning?

Yes, but the focus changes:

Musisi dan desainer berbagi portofolio mereka …
= Musicians and designers share their portfolios …
(active voice; focuses on what they do)
Portofolio mereka dibagikan di konser kecil …
= Their portfolios are distributed / handed out at the small concert …
(passive voice; focuses on the portfolios, not the people doing the sharing)

dibagikan suggests more of a distribution (possibly to an audience), while berbagi portofolio can include showing, presenting, or sharing in a broader sense.