Learn Hardcore Malay: Dia menyatakan bahawa bil restoran itu akan saya bayar. - He/She states that the restaurant bill will be paid by me.

Malay often fronts the object for focus or topicalization. The pattern here is sometimes called the “short passive” or “object-fronting” construction:

Bil restoran itu akan saya bayar = “That restaurant bill, I will pay (it).”
It emphasizes the bill (what will be paid), rather than who pays.
The neutral active order would be Saya akan membayar bil restoran itu.

Is this sentence passive or active?

Functionally, it behaves like a passive (the object is in front and is being highlighted), but morphologically there’s no passive prefix on the verb. Grammars often call it “passive type 2/short passive”:

Short passive/object-fronting: Bil restoran itu akan saya bayar.
Canonical passive with di-: Bil restoran itu akan dibayar (oleh saya).
Active: Saya akan membayar bil restoran itu.

Why is the verb in the bare form bayar and not membayar?

In the short passive/object‑fronting pattern, the verb stays in its base form:

Correct: ... akan saya bayar.
Not used here: ... akan saya membayar. Use membayar when the subject precedes the verb in a regular active clause:
Saya akan membayar bil restoran itu.

Can I rephrase it more plainly as Dia menyatakan bahawa saya akan membayar bil restoran itu?

Yes. That’s a perfectly natural, neutral active sentence. The difference:

... bil restoran itu akan saya bayar = focuses the bill.
... saya akan membayar bil restoran itu = neutral focus on the action/subject.

What is the role of bahawa? Do I need it?

Bahawa is a complementizer meaning “that,” introducing the reported clause after verbs like menyatakan (“to state”).

Formal/standard: Dia menyatakan bahawa ...
Often dropped in speech: Dia menyatakan ...
Colloquial with yang after verbs like kata/cakap: Dia kata yang ... (informal; in careful writing, prefer bahawa or omit it if acceptable).

Can I use the regular passive with di-, like ... akan dibayar oleh saya?

Grammatically yes: Dia menyatakan bahawa bil restoran itu akan dibayar oleh saya. Nuance:

With oleh saya, it sounds quite heavy/formal.
In everyday Malay, people prefer either the neutral active (saya akan membayar...) or the short passive (... akan saya bayar).

Why is itu after bil restoran? Does it just mean “the”?

Itu literally means “that,” and often marks definiteness/specific reference:

bil restoran itu = “that restaurant bill” / “the restaurant bill (we both know about).”
Without itu: bil restoran can be generic or less specific.
ini would mean “this”: bil restoran ini = “this restaurant bill.”

Where does akan go in this kind of sentence?

Common placements you’ll hear/see:

Short passive: Bil restoran itu akan saya bayar. (most standard in writing)
Also heard: Bil restoran itu saya akan bayar. (natural in speech)
Neutral active: Saya akan membayar bil restoran itu. The key is that in the fronting pattern, the verb remains bare (bayar) and akan typically scopes over the whole predicate.

How do I negate this sentence?

Use tidak (not) or belum (not yet) with the fronted pattern like this:

Will not: Dia menyatakan bahawa bil restoran itu tidak akan saya bayar.
Not yet (present perfect-like): Dia menyatakan bahawa bil restoran itu belum saya bayar. Active versions:
Dia menyatakan bahawa saya tidak akan membayar bil restoran itu.
Dia menyatakan bahawa saya belum membayar bil restoran itu.

What exactly does menyatakan mean compared with mengatakan, berkata, and memberitahu?

menyatakan = “to state/declare” (formal, precise).
mengatakan = “to say (that)” (neutral/formal).
berkata/kata = “to say/speak” (often used with direct speech).
memberitahu (seseorang) (bahawa) = “to inform/tell (someone) (that).” Example:
Dia menyatakan/mengatakan bahawa ... (that‑clause)
Dia berkata, ... (quoted speech)
Dia memberitahu saya bahawa ... (tells someone that)

Could I say Dia menyatakan bil restoran itu akan saya bayar without bahawa?

Yes, especially in less formal contexts. After a verb like menyatakan, adding bahawa is stylistically formal/clear, but it can be omitted if the clause boundary is obvious:

Formal: Dia menyatakan bahawa bil restoran itu akan saya bayar.
Acceptable in many contexts: Dia menyatakan bil restoran itu akan saya bayar.

Can I swap saya for other pronouns in this pattern?

Yes. The short passive is most natural with pronouns:

Bil restoran itu akan aku/awak/anda/dia/kami/kita/mereka bayar. Register notes:
saya (polite/formal), aku (informal/intimate), anda (polite/formal but less used in speech), awak/kamu (you; region/register dependent), dia (he/she), beliau (respectful he/she), mereka (they).

What’s the difference between bil, resit, and invois?

bil = a bill you are expected to pay (utilities, restaurant bill).
resit = receipt you receive after paying.
invois = invoice (more formal/business context).

Could I say Bil restoran itu yang akan saya bayar? What does the yang do?

Yes, that adds a focus/cleft meaning: “It’s the restaurant bill that I will pay (not something else).”

Bil restoran itu akan saya bayar = object-fronting focus on the bill.
Bil restoran itu yang akan saya bayar = explicit exclusive focus (“the one that I will pay is the restaurant bill”).