Learn Hardcore Indonesian: Kalau kamu cukup tidur malam ini, besok kamu bisa belajar lebih fokus tanpa harus minum kopi banyak-banyak. - If you sleep enough tonight, tomorrow you can study more focused without having to drink a lot of coffee.

Kalau kamu cukup tidur malam ini, ...
it’s more naturally understood as “if you sleep enough tonight”, because the speaker is talking about a condition: maybe you will sleep enough, maybe you won’t. So here it’s conditional, not a guaranteed “when”.

In “kamu cukup tidur”, what is cukup doing grammatically, and why is it placed before tidur?

Cukup means “enough”, and here it functions like an adverb modifying the verb tidur (“to sleep”).

kamu = you
cukup = enough
tidur = sleep

Literal structure: you – enough – sleep → “you sleep enough”.

In Indonesian, it’s very common to put cukup before the verb:

cukup makan = eat enough
cukup minum = drink enough
cukup tidur = sleep enough

You might also see tidur cukup, but cukup tidur is more natural in this “amount of sleeping” sense.

Could malam ini be put in other positions, and would that change the meaning?

Yes, malam ini (“tonight / this evening”) can move around a bit without changing the basic meaning:

Kalau kamu cukup tidur malam ini, ...
Kalau malam ini kamu cukup tidur, ...
Malam ini, kalau kamu cukup tidur, besok kamu bisa ... (more marked, with a pause after malam ini)

Differences:

Option 1 (original) is the most natural and neutral.
Option 2 puts mild focus on malam ini (“If tonight you sleep enough…”).
Option 3 strongly foregrounds the time; it sounds a bit more dramatic or story-like.

All are grammatically fine; the core meaning is the same.

Why is besok placed at the start of the second clause (besok kamu bisa belajar...)? Can it go elsewhere?

Besok means “tomorrow” and acts as a time adverb. Indonesian time words are quite flexible in position. Possible variants:

Besok kamu bisa belajar lebih fokus... (original)
Kamu besok bisa belajar lebih fokus...
Kamu bisa belajar lebih fokus besok...

Subtle nuances:

Besok kamu bisa...: Slightly emphasizes “tomorrow” at the start (natural and common).
Kamu besok bisa...: Very common in speech; neutral.
Kamu bisa belajar lebih fokus besok: Emphasizes the activity a bit more, with besok as an afterthought.

All three are acceptable; there’s no big meaning change, just different focus.

Why is bisa used here instead of dapat or boleh? What’s the difference?

Bisa, dapat, and boleh all translate to “can” in English but have different nuances:

bisa = can, be able to (ability / possibility)
- Besok kamu bisa belajar lebih fokus = “Tomorrow you can / will be able to study more focused.”
dapat = can, may (more formal; also means “to get/obtain”)
- Besok kamu dapat belajar lebih fokus sounds more formal or written.
boleh = may (permission)
- Besok kamu boleh belajar lebih fokus would mean “Tomorrow you are allowed to study more focused,” which is odd in this context.

So bisa is correct because we’re talking about ability / possibility, not permission, and we’re in a casual tone.

In belajar lebih fokus, is fokus an adjective or a noun? Should it be dengan lebih fokus?

In belajar lebih fokus, fokus works like an adjective / adverb meaning “focused / with focus,” and lebih means “more”:

belajar = to study
lebih = more
fokus = focused

So it’s “study more focused” / “study with more focus”.

You could also say:

belajar dengan lebih fokus

This is a bit more explicit and slightly more formal (“study with more focus”). In everyday speech belajar lebih fokus is perfectly natural and very common.

What does tanpa harus mean exactly, and why do we need both tanpa and harus?

tanpa = without
harus = must / have to

So tanpa harus minum kopi banyak-banyak literally is:

“without having to drink a lot of coffee” (or “without needing to drink a lot of coffee”)

Why both?

tanpa minum kopi banyak-banyak = without drinking a lot of coffee (you don’t do it at all)
tanpa harus minum kopi banyak-banyak = you don’t need to drink a lot of coffee (you might still drink some, but it’s no longer necessary)

So tanpa harus adds the nuance of “no longer necessary / no obligation”, not just “you don’t do it.”

What is going on with minum kopi banyak-banyak? Why is banyak doubled?

minum = to drink
kopi = coffee
banyak = many / much
banyak-banyak (reduplicated) = a lot, loads, plenty

banyak-banyak is the reduplication of banyak to emphasize a large quantity in a casual, often slightly colloquial way. So:

minum kopi banyak = drink a lot of coffee (neutral)
minum kopi banyak-banyak = drink lots and lots of coffee / “so much coffee”

The reduplication banyak-banyak makes it sound more emphatic or informal, a bit like saying “a ton of coffee” in English.

Could we also say banyak minum kopi instead of minum kopi banyak-banyak? Is there any difference?

Yes, banyak minum kopi is also possible:

banyak minum kopi = (to) drink a lot of coffee
minum kopi banyak-banyak = (to) drink lots and lots of coffee

Subtle differences:

banyak minum kopi sounds a bit more neutral and can even describe a general habit:
- Dia banyak minum kopi. = He/She drinks a lot of coffee.
minum kopi banyak-banyak is more vivid / emphatic, describing really large amounts in that situation:
In this sentence, minum kopi banyak-banyak nicely matches the idea “you won’t need to chug a ton of coffee to stay focused.”

Do we really need to repeat kamu in besok kamu bisa belajar...? Could we drop the second kamu?

You can drop the second kamu in casual speech:

Kalau kamu cukup tidur malam ini, besok bisa belajar lebih fokus tanpa harus minum kopi banyak-banyak.

This is still understandable, because context tells us who we’re talking about. Indonesian often omits pronouns when they are clear from context.

However, keeping kamu:

makes the sentence a bit clearer and more balanced,
and sounds very natural too.

So both are acceptable; the original version with repeated kamu is perfectly normal.

Is this sentence formal or informal? How would you say it in a more formal way?

The sentence is informal, mainly because of:

kamu = you (casual / neutral, but not formal)

A more formal version might be:

Jika Anda cukup tidur malam ini, besok Anda dapat belajar dengan lebih fokus tanpa harus minum kopi terlalu banyak.

Changes:

Anda instead of kamu (polite / formal “you”)
jika instead of kalau (more formal conditional)
dapat instead of bisa (slightly more formal)
optionally dengan lebih fokus instead of lebih fokus
terlalu banyak (“too much”) instead of banyak-banyak, which sounds more colloquial.