Learn Hardcore Malay: Bayaran tambahan dikenakan jika bagasi berat. - An additional fee is charged if the luggage is heavy.

Dikenakan comes from the verb kena (“to be subject to; to be hit/affected”) with the passive prefix di- and the causative/transitive sense from -kan (via the active form mengenakan).
In this context it means “is imposed/levied/applied.”
The passive is used because the agent (e.g., the airline) is generic or unimportant in the message. It’s common on signs and notices.
Active equivalent: Syarikat penerbangan mengenakan bayaran tambahan… (“The airline imposes an additional fee…”).

Is bayaran the same as caj? Which sounds more natural?

Bayaran = the payment (money paid).
Caj = the fee/charge (what is levied).
Both are widely used; on notices you’ll see either:
Bayaran tambahan (akan) dikenakan…
Caj tambahan (akan) dikenakan… If you want to be precise: use caj for the imposed fee and bayaran for what customers pay—but in practice both appear in this formula.

Why is there no subject like anda (“you”) or the agent?

The sentence is a passive with an omitted agent, a standard way to state rules. The implied agent is the service provider (e.g., airline). If you want an explicit agent:

Bayaran tambahan dikenakan oleh syarikat penerbangan jika… Or make “you” the patient:
Anda akan dikenakan bayaran tambahan jika…

Do I need akan to talk about the future?

No. Malay doesn’t need a tense marker for general rules; time is inferred. Adding akan makes the future timing explicit:

Without: Bayaran tambahan dikenakan… (generic rule)
With: Bayaran tambahan akan dikenakan… (explicitly “will be imposed”)

Why isn’t there adalah before berat?

Malay adjectives can function as predicates without a copula. So bagasi berat literally functions as “the baggage [is] heavy.” Using adalah with adjectives is usually unnecessary and can sound stiff:

Natural: Bagasi berat.
Odd/stiff: Bagasi adalah berat. Use adalah mainly before nouns: Bagasi adalah tanggungjawab penumpang.

Should it be jika or kalau?

Both mean “if.”

Jika is more formal and common in written notices.
Kalau is informal/colloquial speech.
So your sentence uses the appropriate formal jika.

Do I need yang or itu in bagasi berat?

Not here. Bagasi berat is a full clause (“[the] baggage is heavy”).

Bagasi yang berat means “the heavy baggage” (a noun phrase), which changes the structure. For example:
- Clause: … jika bagasi berat. (“… if the baggage is heavy.”)
- Noun phrase: … untuk bagasi yang berat. (“… for heavy baggage.”)

How do I indicate who the fee applies to?

Add a recipient with kepada (or formal ke atas):

Bayaran tambahan dikenakan kepada penumpang yang bagasinya berat.
Very formal: … dikenakan ke atas penumpang…
If you keep it impersonal (sign style), you can omit the recipient as in the original.

How can I make the weight condition explicit?

Use a limit with melebihi (“exceed”) or lebih daripada:

Bayaran tambahan dikenakan jika bagasi melebihi 20 kg.
Bayaran tambahan akan dikenakan jika berat bagasi melebihi had yang ditetapkan.

How do I say “too heavy,” “heavier,” or “light”?

Too heavy: terlalu berat
Heavier (comparative): lebih berat
Light: ringan
Example: Bayaran tambahan dikenakan jika bagasi terlalu berat.

What’s a natural casual version?

Kalau beg awak berat, kena bayar lebih.
Notes:
beg (bag) is common in speech.
kena colloquially means “have to/must” (not the passive marker here).
bayar lebih = “pay more.”

How do I say there’s no extra fee?

Tiada bayaran tambahan dikenakan. (there is no additional fee imposed)
Bayaran tambahan tidak dikenakan. (additional fee is not imposed)
Both are fine; tiada is often used for existence (“there is no…”).

Is bagasi singular or plural? When should I use beg?

Bagasi is a mass/collective noun for luggage and doesn’t change for plural. Context tells you if it’s one piece or many.
Beg refers to an individual bag. For specific pieces, say sebuah beg, dua beg, etc.
Formal/sign context prefers bagasi; casual speech often says beg.

Any quick pronunciation tips for the sentence?

Bayaran: ba-ya-ran (a as in “father”; r is lightly tapped)
tambahan: tam-ba-han (h is pronounced)
dikenakan: di-ke-na-kan (the e in ke is a schwa /ə/)
jika: ji-ka (j like English “j”)
bagasi: ba-ga-si (g is hard, as in “go”)
berat: be-rat (the e is a schwa /bə-/; final t is crisp)
Malay has even stress; keep syllables clear and steady.