Kawan saya merancang satu kejutan kecil untuk hari lahir gurunya.

In Malay, possessors usually come after the noun they own.

• kawan saya = my friend (literally: friend my)
• rumah saya = my house
• buku dia = his/her book

So kawan (friend) comes first, and saya (I/my) comes after it to show possession.
Saya kawan would mean something like I (am a) friend, not my friend.

It can mean either, depending on context.

Malay usually doesn’t mark plural with an ending like English -s.

• kawan saya can be my friend (one person)
• kawan-kawan saya clearly means my friends (more than one)
• In casual speech, people sometimes just say kawan saya even when they mean more than one; the listener understands from context.

In your sentence, we usually imagine one friend, but it could be plural if the wider context mentions a group.

Rancang is the root verb (to plan), and merancang is the active verb form made with the prefix meN-.

• rancang – base form (you might see this in dictionaries, headlines, or after certain particles like nak, sudah, akan)
• merancang – normal, fully inflected verb used in sentences:
  
  • Dia merancang sesuatu. – He/She is planning something.

In a full sentence like yours, merancang is the natural choice:
Kawan saya merancang… = My friend is/was planning…

Malay typically doesn’t use a separate verb “to be” (like is, am, are) before verbs.

• English: My friend *is planning…*
• Malay: Kawan saya merancang…

The tense (present, past, future) is worked out from context or from time words:

• tadi – earlier, just now
• semalam – last night
• esok – tomorrow
• akan – will (future marker)

So you could say:

• Kawan saya merancang… – My friend is/was planning… (context decides)
• Kawan saya akan merancang… – My friend will plan…

Satu literally means “one”, but in many sentences it functions like the English “a/an”.

• satu kejutan kecil = one small surprise or a small surprise

Often, Malay can omit this:

• Kawan saya merancang kejutan kecil… – My friend planned a small surprise… (still natural)

Adding satu can make it feel a bit more specific/emphatic (one particular surprise), but it isn’t always necessary.

Both are possible:

• satu kejutan kecil – literally one small surprise
• sebuah kejutan kecil – uses the classifier buah, which often goes with general/countable things

In practice:

• sebuah kejutan kecil often sounds a bit more polished/natural in careful writing or speech.
• satu kejutan kecil is also acceptable and understandable, especially in everyday conversation.

So you could say either:

• Kawan saya merancang satu kejutan kecil…
• Kawan saya merancang sebuah kejutan kecil…

Malay usually puts adjectives after the noun they describe.

• kejutan kecil – small surprise (literally surprise small)
• buku baru – new book
• rumah besar – big house

So the normal order is:

noun + adjective

Putting kecil first (e.g. kecil kejutan) would be wrong in standard Malay.

Untuk means “for” (indicating purpose or benefit).

• …kejutan kecil untuk hari lahir gurunya.
  – …a small surprise for his/her teacher’s birthday.

Other possibilities:

• bagi – also “for”, slightly more formal or written
• kepada – usually “to”, often for giving something to someone

In this sentence:

• untuk hari lahir gurunya is the most natural way to say for his/her teacher’s birthday.
• bagi hari lahir gurunya is possible but less common in everyday speech.

All are related to “birthday”:

• hari lahir – literally day of birth, common and neutral
• hari jadi – also widely used, especially in Malaysia, more colloquial
• ulang tahun – literally anniversary (used for birthdays and other anniversaries), feels a bit more formal

Examples:

• hari lahir gurunya – his/her teacher’s birthday
• hari jadi saya – my birthday
• ulang tahun perkahwinan – wedding anniversary

In your sentence, hari lahir gurunya = his/her teacher’s birthday.

Gurunya is made of:

• guru – teacher
• -nya – a suffix often meaning “his/her/its” or “the” (definiteness)

So gurunya usually means:

• his/her teacher
  
  • Here, it most naturally refers to the friend’s teacher (the teacher of my friend).

However, -nya can sometimes just make a noun definite, like the teacher (when the owner is already known from context). Without more context, English speakers usually translate it as:

• for his/her teacher’s birthday

Yes, but the meaning shifts slightly.

• hari lahir gurunya – literally the birthday of his/her teacher
• hari lahirnya – his/her birthday (the -nya refers to the most relevant person in context)

So:

• If the focus is clearly on the teacher, hari lahir gurunya is clearer.
• hari lahirnya could refer to my friend’s birthday or the teacher’s birthday, depending on context.

There are several words:

• kawan – friend; very common, neutral, everyday
• rakan – friend/colleague/associate; sounds more formal (used in official writing, workplaces)
• sahabat – close friend; suggests a deeper, more intimate friendship

Your sentence:

• Kawan saya merancang… – My friend planned… (normal, everyday tone)

You could say Sahabat saya merancang… if you want to emphasise a close friendship.

Grammatically, yes, but the level of formality changes.

• saya – polite, neutral; used with strangers, teachers, at work, in writing
• aku – informal, used with close friends/family, or in casual contexts

So:

• Kawan saya merancang… – neutral/polite
• Kawan aku merancang… – more casual and intimate

Choose based on who you’re talking to and the situation.