Kalau formulir ini belum diisi, Anda harus kembali ke loket.

Kalau means if in this sentence.

It introduces a condition:

• Kalau formulir ini belum diisi = If this form has not been filled in yet

A native speaker might also use jika for if, but kalau is very common in everyday Indonesian and sounds natural in speech.

So:

• kalau = common, everyday if
• jika = a bit more formal

This is a very important difference in Indonesian.

• belum = not yet
• tidak = not

So:

• belum diisi = has not been filled in yet
• tidak diisi = is not filled in / is not being filled in / not filled, depending on context

In this sentence, belum is used because the idea is that the form still needs to be filled in. It suggests something expected has not happened yet.

A useful pattern:

• sudah = already
• belum = not yet

Example:

• Formulir ini sudah diisi. = This form has already been filled in.
• Formulir ini belum diisi. = This form has not been filled in yet.

Diisi comes from the root isi, which relates to contents or to fill.

With the prefix di-, it becomes a passive verb:

• isi = fill / content
• mengisi = to fill in, to fill out
• diisi = filled in / filled out / be filled in

So:

• Anda mengisi formulir = You fill out the form.
• Formulir diisi = The form is filled out.

In your sentence, belum diisi means has not yet been filled in.

Because the sentence focuses on the form, not on who fills it out.

Compare:

• Kalau Anda belum mengisi formulir ini... = If you have not filled out this form...
• Kalau formulir ini belum diisi... = If this form has not been filled out...

Both are possible, but they focus on different things:

• mengisi version focuses on you
• diisi version focuses on the form

In notices, instructions, and official language, Indonesian often uses this kind of passive structure because it sounds neutral and formal.

Indonesian often puts the thing being talked about first, followed by its description or action.

So:

• formulir ini = this form
• belum diisi = not yet filled in

Together:

• formulir ini belum diisi = this form has not yet been filled in

This is very normal Indonesian word order.

You can think of it like:

[subject/topic] + [predicate]

Here:

• formulir ini = subject/topic
• belum diisi = predicate

Anda is the polite/formal word for you.

It is commonly used in:

• official notices
• customer service
• public instructions
• formal writing

That fits this sentence well, because it sounds like something said at an office or service counter.

Compare:

• Anda = formal/polite you
• kamu = informal you
• saudara = formal, but more old-fashioned or specific
• often Indonesian also drops you entirely if it is understood from context

So this sentence sounds appropriately polite and official.

Yes. Harus means must or have to.

So:

• Anda harus kembali ke loket = You must / have to return to the counter

It is a strong requirement, not just a suggestion.

Compare:

• harus = must, have to
• perlu = need to
• sebaiknya = should, it would be better to

Because this is likely an instruction in an official setting, harus makes sense.

Kembali means return or go back.

• kembali = return / go back
• ke = to
• loket = counter / service window / ticket window

So:

• kembali ke loket = return to the counter

This probably refers to a service desk, administrative window, or registration counter in a public office, hospital, station, etc.

Loket usually refers to a service counter or window, especially one where customers submit documents, buy tickets, or handle administrative matters.

It is often more specific than just desk.

Common contexts:

• train or bus ticket windows
• government offices
• hospital registration counters
• bank or payment counters

So loket is best understood as counter or service window.

Because Indonesian does not need a separate word corresponding to English out here.

English says:

• fill out a form
• fill in a form

Indonesian simply uses:

• mengisi formulir
• formulir diisi

The verb isi / mengisi / diisi already covers the idea of filling in a form. So there is no separate little word like out.

This is very common when translating phrasal verbs from English: Indonesian often expresses the idea with a single verb or a verb with affixes.

Yes.

• Kalau formulir ini belum diisi, Anda harus kembali ke loket.
• Jika formulir ini belum diisi, Anda harus kembali ke loket.

Both are correct.

The difference is mostly style:

• kalau = more everyday, conversational
• jika = more formal, written, official

Since the sentence already contains formal elements like Anda and loket, jika would also sound perfectly natural.

Yes, it could.

For example:

• Kalau formulir ini belum diisi, harus kembali ke loket.

This can still be understood as If this form has not been filled in, you must return to the counter, especially in a sign or instruction.

Indonesian often omits subjects when they are obvious from context. However, including Anda makes the instruction clearer and more polite.

So:

• with Anda = explicit, polite, official
• without Anda = shorter, still natural in notices

It sounds formal to neutral-formal.

Things that make it formal:

• Anda instead of kamu
• the passive belum diisi
• the office-related word loket

This sounds like something from:

• a public notice
• an office worker
• a hospital or government office
• a written instruction

A casual version might be more like:

• Kalau formulir ini belum kamu isi, kamu harus balik ke loket.

That version is much more informal because of kamu and balik.

The sentence has two parts:

1. Kalau formulir ini belum diisi

   • conditional clause
   • If this form has not yet been filled in

2. Anda harus kembali ke loket

   • main clause
   • you must return to the counter

So the overall structure is:

If X, then Y

More literally:

• Kalau = If
• formulir ini = this form
• belum diisi = has not yet been filled in
• Anda = you
• harus = must
• kembali ke loket = return to the counter

That makes it a very typical Indonesian conditional sentence.