Learn Hardcore Indonesian: Karena lembur malam ini, saya makan malam di kantor. - Because of overtime tonight, I eat dinner at the office.

Reason first: Karena lembur malam ini, saya makan malam di kantor.
Reason last: Saya makan malam di kantor karena lembur malam ini. Both are natural.

Is the comma necessary after the initial clause?

Yes, when the karena-clause comes first, a comma is standard: Karena ..., [comma] .... If the karena-clause comes after the main clause, you normally don’t use a comma: ..., karena ....

Is lembur a noun or a verb?

Both, depending on context.

As a verb (to work overtime): Saya lembur malam ini.
As a noun (overtime as a thing): Karena lembur malam ini, ... You’ll also hear kerja lembur or bekerja lembur for “work overtime.”

Can I say Karena saya lembur malam ini instead of Karena lembur malam ini?

Yes. Karena saya lembur malam ini, ... is slightly more explicit (it states the subject), but both are natural and common.

Does malam ini modify lembur or makan malam here?

It modifies lembur. The idea is “because of tonight’s overtime.” If you worry about ambiguity, you can write Karena saya lembur malam ini, saya makan malam di kantor to make it crystal clear.

Why is malam repeated (lembur malam ini and makan malam)? Isn’t that redundant?

No. Makan malam is a set phrase meaning “to have dinner,” not literally “eat at night.” So having malam in both places is normal: one marks the time of the overtime, the other is the fixed expression for dinner.

Is makan malam one word or two? Are there alternatives?

Two words: makan malam. Other mealtime pairs are sarapan (breakfast, one word) and makan siang (lunch, two words). A more formal synonym for dinner is santap malam.

How is tense expressed? Does saya makan malam mean I am eating or I will eat?

Indonesian verbs don’t inflect for tense. Saya makan malam can be present, near future, or even habitual. Time words like malam ini, tadi malam, besok provide the timeframe; context does the rest.

Why is it di kantor and not ke kantor?

Di marks location (at/in), while ke marks movement (to). You eat at a place: makan malam di kantor. If you talk about going somewhere, use ke: Saya pergi ke kantor untuk makan malam.

Do I need an article like “the” before kantor?

Indonesian has no articles. Di kantor can mean “at the office,” “at my office,” or “at the office building,” depending on context. If needed, specify: di kantor saya, di kantor perusahaan, etc.

Can I drop the subject pronoun saya?

Yes, if context makes it clear: Karena lembur malam ini, makan malam di kantor. In formal or less context-rich situations, keep saya. Also note register: saya (neutral/formal), aku (informal), gue (very informal, Jakarta).

Is pada malam ini better than just malam ini?

In everyday speech, malam ini is standard. Pada malam ini is more formal/written. Avoid di malam ini in standard prose (though di malam hari = “at night” is fine generically).

Are there other ways to say “because,” and do they differ in tone?

Yes:

sebab (formal/literary): Sebab saya lembur malam ini, ...
gara-gara (colloquial, often negative nuance): Gara-gara lembur malam ini, ...
soalnya (very colloquial, “the reason is”): Saya makan malam di kantor, soalnya saya lembur malam ini.

Is karena itu the same as karena?

No. Karena itu means “therefore/as a result,” not “because.” Example: Saya lembur malam ini; karena itu, saya makan malam di kantor.

Can I front the location for emphasis?

Yes: Di kantor, saya makan malam karena lembur malam ini. Fronting di kantor emphasizes the location.

Should it be malam ini or ini malam?

Use malam ini. Demonstratives like ini follow the noun in Indonesian. Ini malam is nonstandard in Indonesian (though you’ll see different patterns in some Malay varieties). You can also say nanti malam (“later tonight”), which emphasizes “later from now.”

Any quick pronunciation tips?

lembur: the e is a schwa (like the a in “about”), r is tapped/trilled.
saya: roughly “SAH-yah.”
kantor: “KAN-tor,” with a clear o and a pronounced final r.