Learn Hardcore Swahili: Asha alichagua kiti cha mbele; chaguo lake lilimtuliza. - Asha chose the front seat; her choice made her calm.

It’s the associative linker “of,” and it agrees with the noun class of the head noun. Since kiti is class 7 (ki-/vi-), its associative linker is cha, so kiti cha mbele = “seat of the front” → “front seat.”
Examples:

kiti cha plastiki = plastic chair
kitabu cha Kiswahili = Swahili book

Why is it lake (in chaguo lake) and not yake?

Possessives agree with the noun class of what is possessed. Chaguo is class 5 (ji-/Ø, plural class 6 ma-), and class 5 uses the possessive stem la-, so “his/her” is lake.

Singular: chaguo lake = his/her choice (class 5)
Plural: machaguo yake = his/her choices (class 6 uses ya- → yake)

Why does lilimtuliza start with what looks like “lili-”? Is that a mistake?

Not a mistake. It’s two separate morphemes back-to-back:

li- (subject agreement for class 5, matching chaguo)
-li- (past tense)
So you get li-li- → “lili-”. Full breakdown: li- (class 5 subject) + -li- (past) + -m- (him/her object) + tuliz (calm) + -a (final vowel) → lilimtuliza.

Who does the -m- object marker in lilimtuliza refer to?

It’s the third-person singular object “him/her,” referring back to Asha. The clause means “(it) calmed her.”

Why is there no separate word for “she” in Asha alichagua?

Swahili encodes the subject on the verb. a- is the 3rd person singular subject marker (“he/she”), and -li- is past tense: a-li-chagua = “she/he chose.” You only add yeye (“she/he”) for emphasis or contrast.

Does Swahili mark “the” vs “a”? How do we know if kiti is “a seat” or “the seat”?

Swahili has no articles. kiti can mean “a seat” or “the seat” depending on context. Here, the context makes it clear which is meant.

What’s the difference between tulia and tuliza?

tulia: intransitive, “to become calm/settle down” (no direct object).
tuliza: causative, “to calm (someone/something).”
In the sentence, we need the causative: … lilimtuliza = “(it) calmed her.”

Where does the noun chaguo come from, and what’s its plural?

It’s a nominalization of the verb chagua (“to choose”), producing a class 5 noun meaning “choice.”

Singular: chaguo (class 5)
Plural: machaguo (class 6)

If I make “seat(s)” plural, what else changes?

Plural of kiti is viti (class 8).
The associative linker changes accordingly: viti vya mbele (“front seats”).
If you made the seats the subject, the verb would agree in class 8: viti vya mbele vilimtuliza (“the front seats calmed her”). But in the original sentence, the subject is chaguo, so the agreement remains with class 5.

Why is it lilimtuliza and not kilimtuliza?

Because the subject of the second clause is chaguo (class 5), which takes the subject marker li-. Ki- would agree with a class 7 subject like kiti. If the subject were kiti, you’d use kilimtuliza.

Can I drop the object marker and say lilituliza?

If you drop -m-, you lose the explicit “her.” lilituliza just says “(it) calmed.” To keep “her,” you either keep the object marker (lilimtuliza) or add an explicit pronoun for emphasis: lilimtuliza yeye (“it calmed her [in particular]”).

What does mbele mean here, and do I ever need mbele ya?

mbele = “front/ahead.”

kiti cha mbele = “front seat” (no extra preposition).
mbele ya means “in front of (something/someone)”: mbele ya nyumba = “in front of the house.”

Could I use a different word for “choice,” like uamuzi?

Yes, with a slight nuance: uamuzi = “decision” (class 14), a bit more formal/decisive than chaguo (“choice”). Agreement changes with noun class:

uamuzi wake ulimtuliza (class 14 subject marker u- → past -li- gives uli-).

Why a semicolon here? Could I write this another way?

A semicolon neatly links two closely related clauses. You could also write:

Two sentences: Asha alichagua kiti cha mbele. Chaguo lake lilimtuliza.
With “and”: Asha alichagua kiti cha mbele, na chaguo lake lilimtuliza.
In narrative style, you sometimes see -ka- for “and then”: … chaguo lake likamtuliza.

How does the verb alichagua break down?

a- = 3rd person singular subject (“he/she”)
-li- = past tense
chagu- … -a = verb stem chagua (“choose”)
Result: alichagua = “she/he chose.”

Any tips on pronouncing chagua and chaguo?

chagua: cha-GU-a (all vowels pronounced; “g” as in “go”).
chaguo: cha-GWO (the “u+o” often comes out as a smooth “-gwo”).
mbele: MBE-le (the initial “m” is part of the syllable; say “m-be-le”).

How do the main agreement/linker pieces change with other common noun classes?

Very briefly (singular → plural):

Class 7/8 (ki-/vi-): associative cha/vya; subject markers ki-/vi-.
Class 5/6 (Ø-/ma- like chaguo/machaguo): associative la/ya; subject markers li-/ya-.
Class 9/10 (N-/N-): associative ya/za; subject markers often i-/zi-.
Agreement must match the class of the head noun (the thing possessed or the subject).