Kalau saya ada baki satu ringgit lagi, saya mahu beli biskut di kaunter itu.

Yes. Kalau means if and is very common in everyday Malay.

In this sentence, Kalau saya ada baki satu ringgit lagi... introduces the condition:

• If I have one ringgit left over...

A slightly more formal alternative is jika, but kalau is very natural in speech and informal writing.

Malay often keeps the subject in both parts of a sentence for clarity:

• Kalau saya ada baki satu ringgit lagi, saya mahu beli biskut...

Literally:

• If I have one ringgit left, I want to buy biscuits...

Even though English sometimes allows omission or restructuring, Malay usually sounds clearer and more natural when the subject is stated again in the main clause.

It helps to break it down:

• ada = have / there is
• baki = remainder / balance / leftover
• satu ringgit = one ringgit
• lagi = more / still / extra, depending on context

So ada baki satu ringgit lagi means something like:

• have one ringgit left
• have a remaining balance of one ringgit

This is a very Malay way of expressing the idea of money being left over after spending.

Not in this sentence.

Lagi can mean several things depending on context, including:

• again
• more
• still
• another

Here, it gives the sense of still / remaining / extra.

So baki satu ringgit lagi suggests:

• one ringgit still left
• one more ringgit remaining

That is why the sentence means If I still have one ringgit left over..., not If I have one ringgit again...

Both are possible in Malay.

• satu ringgit = one ringgit
• seringgit = a ringgit / one ringgit

The prefix se- often means one:

• seekor = one animal
• sebuah = one item
• seringgit = one ringgit

In practice, satu ringgit is very clear and common, especially for learners. Seringgit is also natural.

Because after a modal or helper-like verb such as mahu, Malay usually uses the base verb:

• mahu beli = want to buy
• mahu makan = want to eat
• mahu pergi = want to go

Using membeli is possible in some contexts, especially in more formal style, but mahu beli is the more straightforward and natural pattern for everyday Malay.

All can relate to wanting, but they differ in tone and register.

• mahu = want; standard and neutral
• nak = want; very common in casual speech
• ingin = wish/desire; more formal or literary

So:

• saya mahu beli biskut = neutral/standard
• saya nak beli biskut = casual and very common
• saya ingin membeli biskut = more formal

In this sentence, mahu is perfectly normal.

Malay does not need an equivalent of English to in this structure.

English:

• I want to buy biscuits

Malay:

• saya mahu beli biskut

So after mahu, the next verb simply appears in its basic form.

Malay nouns usually do not have to change form for singular vs plural when the meaning is already clear from context.

So:

• biskut can mean a biscuit or biscuits
• context tells you which is meant

Plural reduplication like biskut-biskut exists, but it is not always necessary. In a sentence like this, biskut is enough and sounds natural.

Di is a preposition meaning at, in, or on for locations.

So:

• di kaunter itu = at that counter

Breakdown:

• di = at
• kaunter = counter
• itu = that

Malay uses di before places:

• di rumah = at home
• di kedai = at the shop
• di kaunter itu = at that counter

In Malay, demonstratives normally come after the noun:

• kaunter itu = that counter
• biskut ini = this biscuit / these biscuits
• rumah itu = that house

So the order is:

• noun + ini/itu

This is different from English, where this and that usually come before the noun.

Yes, it is used in Malay, but it is a loanword from English counter.

Malay has many borrowed words, especially for modern objects and places. Kaunter is a normal word in everyday Malay, especially in shops, banks, clinics, and service areas.

It is understandable and basically natural, but a native speaker might also say:

• Kalau saya ada baki seringgit lagi, saya nak beli biskut di kaunter itu.
• Kalau saya masih ada baki satu ringgit, saya mahu beli biskut di kaunter itu.

A few notes:

• nak is more conversational than mahu
• seringgit is a compact alternative to satu ringgit
• masih can make the idea of still having some money left a bit clearer

But the original sentence is still a good, valid Malay sentence for learning purposes.