Learn Hardcore Indonesian: Ibu membeli deterjen baru; deterjen itu wangi sekali. - Mother buys new detergent; that detergent smells very fragrant.

Mother (the speaker’s own mother), used like a proper name and capitalized.
A respectful title for an adult woman (like Mrs./Ma’am), e.g., Ibu Sari.
A polite second-person pronoun when addressing an older woman. In this standalone sentence, it most naturally reads as “Mother” (the speaker’s mother), but context ultimately decides.

How do I say “my mother” explicitly (and how about “a mother”)?

“my mother”: ibu saya (neutral) or ibuku (more intimate). Note the lowercase ibu when it’s a common noun with a possessor.
“a mother (an adult woman/mom)”: seorang ibu.
As a title with a name: Ibu [Name] (e.g., Ibu Sari).

Why is membeli used instead of beli?

membeli is the formal active transitive form built from the root beli with the meN- prefix (here it surfaces as mem- before the consonant b).
beli without the prefix is common and perfectly natural in casual speech: Ibu beli deterjen baru.
Use membeli in writing or more formal contexts.

Is this past or present? How is tense shown?

Indonesian verbs don’t change for tense. Ibu membeli... can mean past, present, or habitual. Add time/aspect words if needed:

Past/time: tadi, kemarin
Completed: sudah / telah
Progressive: sedang
Future: akan Examples: Ibu sudah membeli..., Ibu sedang membeli..., Kemarin Ibu membeli...

Why is it deterjen baru (adjective after noun), not baru deterjen?

Adjectives typically follow nouns in Indonesian: deterjen baru = “new detergent.” When baru comes before a verb phrase, it’s an adverb meaning “just/only then,” e.g., baru datang (“just arrived”). baru deterjen would not mean “new detergent” and sounds odd unless you’re saying something like “only detergent.”

What does itu do in deterjen itu?

itu is the distal demonstrative (“that”) and often marks definiteness (“the”). deterjen itu means “that/the detergent,” usually referring back to a previously mentioned item. The proximal counterpart is ini (“this”). A more formal “aforementioned” is tersebut.

Why isn’t there an “is” before wangi sekali?

Indonesian doesn’t need a copula with adjectives. Deterjen itu wangi sekali literally works as “[That] detergent very fragrant.” Use adalah mainly with noun-predicate sentences; don’t use it with adjectives like wangi.

What’s the nuance of wangi vs harum (and how about bau)?

wangi: pleasantly fragrant, general and common.
harum: pleasantly fragrant too, slightly more refined/poetic; common for flowers/perfume.
bau: “smell/odor” (noun) or “smelly” (adjective, usually negative). For “very smelly,” say bau sekali; for a pleasant smell as a noun, you can say harum or wanginya (“the fragrance”).

How strong is sekali? What are alternatives?

sekali after an adjective = “very”: wangi sekali.
Formal preposed options: sangat wangi, amat wangi.
Informal: wangi banget.
“Too (excessively)”: terlalu wangi.
In negatives: tidak wangi sama sekali = “not fragrant at all.” Note: sekali can also mean “once” with verbs/numbers (e.g., sekali = “one time”), but here it’s the intensity adverb.

Is the semicolon necessary here?

No. A period is most common: Ibu membeli deterjen baru. Deterjen itu wangi sekali. A semicolon is fine to show a close link. If you want to state cause/result explicitly, use a connector:

Cause: Karena deterjen itu wangi sekali, Ibu membelinya.
Result: Deterjen itu wangi sekali, makanya Ibu membelinya.

Can I avoid repeating deterjen in the second clause?

Yes:

Deterjennya wangi sekali. Here -nya marks definiteness (often “the”) or “its/her,” depending on context.
You can also say Itu wangi sekali (“That is very fragrant”) if the referent is obvious, but it can be vague; deterjennya or deterjen itu is clearer.

Should I use yang, as in deterjen yang baru?

deterjen baru: plain description “a new detergent.”
deterjen yang baru: “the one that is new,” often contrastive (as opposed to an old one).
Relative clause: deterjen yang wangi sekali = “the detergent that is very fragrant.”
You could also combine definiteness: Deterjen baru itu wangi sekali = “The new detergent is very fragrant.”

Why is it spelled deterjen, not detergen?

The standard Indonesian spelling (per KBBI) is deterjen. You may see detergen or English detergent informally, but deterjen is the recommended form.

Would you say sebuah deterjen baru?

Usually no. For items like detergent, Indonesians specify the packaging/unit:

sebungkus deterjen (a packet)
sebotol deterjen cair (a bottle of liquid detergent)
sekotak / sekaleng / sepaket, etc., depending on the container sebuah suits countable objects like sebuah rumah (a house), not mass/packaged goods.

How would I say this in the passive or with “buy for”?

Passive: Deterjen baru itu dibeli Ibu; deterjen itu wangi sekali. (or ... dibeli oleh Ibu)
“Buy for [someone]”: use membelikan: Ibu membelikan deterjen baru (untuk saya).