Learn Hardcore Indonesian: Suatu hari saya akan berlibur di pulau kecil itu. - One day I will go on vacation on that small island.

Suatu hari literally means a/one particular day, and in this kind of sentence it’s best translated as “one day / someday” (a vague time in the future, not a specific date).

So:

hari = day (neutral)
suatu hari = one (unspecified) day, someday

You can say Saya akan berlibur di pulau kecil itu suatu hari, but that slightly shifts the emphasis. Putting suatu hari at the front makes it sound more like storytelling or a reflective statement: “One day, I will…”

Can I say satu hari instead of suatu hari? What’s the difference?

They look similar but are used differently:

satu hari = one day in a more literal, countable sense
- e.g. Saya bekerja selama satu hari. = I worked for one day.
suatu hari = one day / someday in a vague, story-like, or non‑specific sense
- e.g. Suatu hari saya akan berlibur di pulau kecil itu. = One day I will go on vacation on that small island.

If you say:

Suatu hari saya akan berlibur… → “One day / Someday I will go on vacation…”
Satu hari saya akan berlibur… → grammatically possible, but it sounds more like you’re stressing the duration of the vacation (for one day) or it just sounds a bit odd as a prediction.

For “someday” in the future, suatu hari is the natural choice.

Is akan necessary to express the future here? Can I say Suatu hari saya berlibur di pulau kecil itu?

Indonesian doesn’t need a special future tense, so akan is optional in many contexts.

Suatu hari saya akan berlibur di pulau kecil itu.
→ Clear future meaning, like “One day I will go on vacation on that small island.”
Suatu hari saya berlibur di pulau kecil itu.
→ Still understandable as future because of suatu hari, but it can sound:
- Less explicit about intention, or
- Like you’re narrating a story about the past (“One day I went on vacation…”) depending on context.

Using akan:

makes the sentence clearly future
often adds a nuance of plan / intention

So here, akan is very natural and slightly clearer for learners.

What is the difference between berlibur, libur, and liburan?

All come from the root libur (holiday / time off), but they behave differently:

libur (adjective / verb-like)
- As an adjective: Hari ini saya libur. = Today I’m off / I have a day off.
- As a verb-like predicate: Sekolah libur besok. = School is off tomorrow.
liburan (noun)
- Means holiday, vacation (the event/period)
- Saya suka liburan. = I like vacations.
- Liburan saya menyenangkan. = My vacation was fun.
berlibur (verb)
- Means to go on vacation / to be on vacation
- Saya akan berlibur di pulau kecil itu. = I will go on vacation on that small island.
- Pattern: ber-
  - noun → verb “to do / have that thing”

In your sentence, berlibur is the right choice because you’re talking about the action of going on vacation.

Why is it di pulau kecil itu and not ke pulau kecil itu?

di and ke both relate to place but have different roles:

di = at / in / on (location, where something happens)
ke = to (direction, where you are going)

Compare:

Saya akan berlibur ke pulau kecil itu.
→ Focus on going to that small island for vacation.
Saya akan berlibur di pulau kecil itu.
→ Focus on being on that small island during the vacation.

In practice, with berlibur:

berlibur ke [tempat] is very common and emphasizes destination.
berlibur di [tempat] is also correct and emphasizes location of the vacation.

Your sentence with di is fine and natural, especially if the idea is “I’ll be spending my vacation on that small island.”

What does itu add in pulau kecil itu? Could I just say pulau kecil?

itu is a demonstrative meaning that (similar to that / the in English, depending on context).

pulau kecil = a small island (general, not specified)
pulau kecil itu = that small island or the small island (specific, you and the listener know which one)

So:

Suatu hari saya akan berlibur di pulau kecil.
→ One day I will go on vacation on a small island (any small island, not specified).
Suatu hari saya akan berlibur di pulau kecil itu.
→ One day I will go on vacation on that small island (a particular one, maybe already mentioned, seen on a map, etc.).

Keeping itu implies the island is known or identifiable in the shared context.

Why is the order pulau kecil itu and not kecil pulau itu?

In Indonesian, the usual order is:

Noun + Adjective + Demonstrative

So:

pulau = island (noun)
kecil = small (adjective)
itu = that (demonstrative)

Correct order: pulau kecil itu

You cannot say kecil pulau itu for “that small island”; that sounds unnatural and ungrammatical.

More examples:

rumah besar itu = that big house
mobil merah ini = this red car
buku baru itu = that new book

Could I drop saya and say Suatu hari akan berlibur di pulau kecil itu?

You can drop saya, and Indonesians do sometimes omit subjects when the context is crystal clear, but:

Suatu hari akan berlibur di pulau kecil itu.
sounds incomplete or like a sentence from a more telegraphic style (e.g. a note, headline, or poetic line).

In ordinary speech or writing, you normally keep the subject pronoun:

Suatu hari saya akan berlibur di pulau kecil itu.

If the subject was already mentioned, you might omit it in later sentences, but the first clear mention usually includes saya, dia, mereka, etc.

Is this sentence formal or informal? How would it change in casual conversation?

With saya and akan, the sentence is neutral to slightly formal, suitable for:

writing
talking to strangers
polite conversation

Casual variants might be:

Suatu hari aku akan liburan di pulau kecil itu.
(using aku, and liburan as a more colloquial verb)
Suatu hari gue bakal liburan di pulau kecil itu.
(very informal Jakarta style: gue for “I”, bakal for “will”)

The core structure stays the same, but:

saya → aku / gue / saya (depends on region and relationship)
akan → akan / bakal / nanti (different informal future markers)
berlibur → berlibur / liburan (both heard, liburan more colloquial as a verb)

Where else can I put suatu hari in the sentence? Is the word order flexible?

Time expressions in Indonesian are quite flexible. All of these are grammatically fine, with slight differences in emphasis:

Suatu hari saya akan berlibur di pulau kecil itu.
→ Emphasis on “One day…”; natural and common.
Saya suatu hari akan berlibur di pulau kecil itu.
→ Emphasis slightly more on “I, one day, will…”. Still correct, just a different rhythm.
Saya akan berlibur di pulau kecil itu suatu hari.
→ Sounds like you’re stating the plan, then adding “someday” at the end.

All three are acceptable. Putting suatu hari at the start (version 1) is probably the most natural in isolation and closest to English “One day, I will…”

Can I say Suatu hari saya akan pergi berlibur di pulau kecil itu? Is that more natural?

Yes, that sentence is correct:

Suatu hari saya akan pergi berlibur di pulau kecil itu.
= One day I will go on vacation on that small island.

Here:

pergi = to go
berlibur = to go on vacation

So pergi berlibur = go on vacation (a common collocation).

Is it more natural?

Both Saya akan berlibur di… and Saya akan pergi berlibur di… are natural.
pergi berlibur just adds an extra sense of movement / departure.
berlibur di… alone already implies the idea of going on vacation, so pergi is optional, not required.

Why is it Suatu hari saya akan berlibur… and not Pada suatu hari saya akan berlibur…? When do I use pada?

Pada is a preposition often used with times and dates, especially in more formal writing:

pada hari Senin = on Monday
pada tahun 2020 = in 2020
pada malam hari = at night

With suatu hari:

Pada suatu hari is a set phrase used a lot in stories and fairy tales, very much like “Once upon a time”.
In everyday speech, people often just say Suatu hari… without pada, and it sounds perfectly natural.

So:

Pada suatu hari, seekor kancil berjalan di hutan.
→ Storytelling: Once upon a time, a mousedeer walked in the forest.
Suatu hari saya akan berlibur di pulau kecil itu.
→ Normal spoken/written Indonesian: One day I will go on vacation on that small island.

You could say Pada suatu hari saya akan berlibur…, but it sounds a bit more formal or literary.