Nikihisi baridi, ninavaa sweta yangu.

Nikihisi can be broken down like this:

• ni- = I
• -ki- = if / when
• -hisi = feel

So Nikihisi literally means if I feel or when I feel.

This is a very common Swahili pattern:

• ni + ki + verb stem

For example:

• Nikiona = if/when I see
• Nikifika = if/when I arrive

In Swahili, -ki- often covers both ideas, depending on context. English usually separates them more clearly, but Swahili often lets the situation decide the best translation.

So:

• Nikihisi baridi can mean If I feel cold
• or When I feel cold

In this sentence, both are natural. The meaning is something like: Whenever I feel cold, I put on my sweater.

Because baridi in this sentence is used with -hisi (to feel), not with to be.

So:

• Nikihisi baridi = if/when I feel cold

Here, baridi means coldness / cold.

Swahili often expresses this idea as feel cold, rather than building it exactly the way English does with adjectives.

Also, baridi is commonly used as a noun-like word meaning cold:

• Kuna baridi = It is cold / There is cold weather
• Nahisi baridi = I feel cold

Ninavaa breaks down like this:

• ni- = I
• -na- = present / habitual / ongoing tense
• -vaa = wear / put on

So ninavaa can mean:

• I wear
• I am wearing
• I put on

In this sentence, the most natural meaning is:

• I put on my sweater or
• I wear my sweater

Because the sentence describes what you do when you feel cold, English often prefers put on here.

The -na- is the common present tense marker in Swahili.

So:

• ninavaa = I wear / I am wearing
• unasoma = you read / you are reading
• anakula = he/she eats / is eating

This tense can express:

• a regular habit
• something happening now
• a general truth

In this sentence, it sounds habitual:

• When I feel cold, I put on my sweater.

Grammatically, kuvaa can cover both to wear and to put on, depending on context.

So ninavaa sweta yangu could be understood as:

• I wear my sweater
• I put on my sweater

In this particular sentence, English usually prefers put on, because it describes an action you take after feeling cold.

If you want learners to sound natural in English, the best translation here is probably:

• When I feel cold, I put on my sweater.

In Swahili, possessives usually come after the noun.

So:

• sweta yangu = my sweater
• kitabu changu = my book
• rafiki yangu = my friend

This is the normal word order:

• noun + possessive

So unlike English, Swahili does not usually put my before the noun.

Swahili possessives agree with the noun class of the thing possessed.

Sweta is usually treated like an N-class noun (like many loanwords), so the possessive takes the matching form:

• yangu = my

That is why you get:

• sweta yangu = my sweater

Compare with other noun classes:

• kitabu changu = my book
• viatu vyangu = my shoes
• mti wangu = my tree

So the form of my changes depending on the noun.

It is a normal Swahili word, but it is a loanword from English sweater.

Swahili has many loanwords, especially for clothing, technology, and modern objects.

For example:

• sweta = sweater
• shati = shirt
• kompyuta = computer

Even though it comes from English historically, it functions as an ordinary Swahili noun.

Swahili does not normally use articles like English a, an, or the.

So:

• sweta yangu can mean my sweater without needing any article

This is very normal in Swahili. The meaning is usually clear from context.

Yes. That would also be correct.

There is a small nuance:

• Nikihisi baridi = if/when I feel cold
• Ninapohisi baridi = when I feel cold

-ki- is often more general and can mean if/when/whenever. -napo- is more specifically when.

So both are good, but:

• Nikihisi baridi, ninavaa sweta yangu sounds like If/Whenever I feel cold, I put on my sweater
• Ninapohisi baridi, ninavaa sweta yangu sounds a bit more directly like When I feel cold, I put on my sweater

Yes, you can.

• Ninavaa sweta = I wear/put on a sweater
• Ninavaa sweta yangu = I wear/put on my sweater

Adding yangu makes it more specific and personal:

• not just any sweater
• my sweater

If the context already makes it obvious whose sweater it is, Swahili can sometimes omit the possessive.

Usually it sounds like a general habit.

• Nikihisi baridi, ninavaa sweta yangu.
• When/Whenever I feel cold, I put on my sweater.

The combination of -ki- and the present tense ninavaa often gives a repeated, habitual meaning.

If you wanted a one-time future-like sense, context would need to make that clear. By itself, this sentence is most naturally understood as something you generally do.