Ni vizuri kuwa mstaarabu unapozungumza na watu wakubwa.

Ni vizuri literally means it is good / it is nice.

In Swahili, ni is often used in simple statements like it is, this is, or X is Y, depending on the context. In this sentence, Ni vizuri is an impersonal expression, so it works like English It is good...

So:

• ni = it is / is
• vizuri = well, nicely, good(ly)

Together, Ni vizuri... means It is good...

Because kuwa means to be, and the sentence is talking about being polite/civilized, not just naming a person.

• kuwa = to be
• mstaarabu = a civilized/polite person

So kuwa mstaarabu literally means to be a civilized/polite person.

In natural English, we would usually translate that more smoothly as:

• to be polite
• to behave politely
• to be courteous

Swahili often uses kuwa + noun/adjective-like word in places where English simply uses an adjective.

Mstaarabu literally refers to a civilized, cultured, or well-mannered person. In many contexts, it can mean:

• polite
• courteous
• well-behaved
• respectful

In this sentence, mstaarabu is best understood as polite or courteous.

So although the word can have a broader meaning than English polite, that is the most natural sense here.

Unapozungumza can be broken down like this:

• u- = you
• -na- = present tense
• -po- = when / as / at the time when
• -zungumza = speak / talk

So unapozungumza means:

• when you speak
• when you are speaking
• while speaking

It is a very common Swahili pattern for when someone does something.

The -po- marks a kind of relative time idea, often translated as:

• when
• while
• as

So unapozungumza is not just you are speaking. It specifically means when you are speaking or as you speak.

Compare:

• unazungumza = you are speaking / you speak
• unapozungumza = when you are speaking / when you speak

That -po- is what gives the clause its when meaning.

It is built from the present tense pattern, but in meaning it can be more general.

Depending on context, unapozungumza can mean:

• when you speak
• when you are speaking
• whenever you speak

So it does not refer to only one exact moment in the present. It can express a general truth or habitual situation too.

In this sentence, it sounds like a general rule: It is good to be polite when speaking to older people.

Normally, na often means and or with. But after verbs of speaking, it can also mean to or with, depending on how English would phrase it.

So:

• kuzungumza na mtu = to speak to someone / to speak with someone

In this sentence:

• unapozungumza na watu wakubwa = when you speak to/with older people

English prefers to here, but Swahili uses na.

Yes, literally it does:

• watu = people
• wakubwa = big / great / important / older

But in context, watu wakubwa usually does not mean physically big people. It more naturally means:

• elders
• older people
• important adults
• senior people

Here it most likely means older people or elders, especially in a social-respect sense.

Because watu is plural, and the describing word has to agree with it.

• mtu mkubwa = an older/big/important person
• watu wakubwa = older/big/important people

This is noun class agreement in Swahili.

For the m-/wa- class:

• singular person: m-
• plural people: wa-

So:

• mtu mzuri = a good person
• watu wazuri = good people

and similarly:

• mtu mkubwa
• watu wakubwa

Yes. Wakubwa can mean:

• big
• senior
• important
• older
• high-ranking

So watu wakubwa can sometimes mean:

• important people
• senior people
• elders

The exact meaning depends on context.

In this sentence, because it talks about how to behave while speaking to them, learners will usually understand it as elders/older people or respected seniors.

Yes, often it would.

• wazee = old people / elders
• watu wakubwa = older people / senior people / important people

The difference is that wazee is more directly elders/old people, while watu wakubwa can be a little broader and can include the idea of senior or important people, not only age.

So both can work, but they are not always exactly identical.

Yes, the order can change.

The original order is:

• Ni vizuri kuwa mstaarabu unapozungumza na watu wakubwa.
• It is good to be polite when you speak to older people.

But Swahili can also put the time clause first:

• Unapozungumza na watu wakubwa, ni vizuri kuwa mstaarabu.

That would still mean the same thing. The original version simply starts with the main idea: It is good...

It sounds like a general rule or piece of advice.

The structure Ni vizuri... often introduces general statements such as:

• It is good to...
• It is advisable to...
• One should...

And unapozungumza can mean when(ever) you speak, not only one single event.

So the whole sentence feels like a general cultural or moral guideline.

A very natural translation could be:

• It is good to be polite when speaking to elders.
• You should be polite when talking to older people.
• It is proper to speak politely to elders.

The most literal translation is closer to:

• It is good to be a polite/civilized person when you speak with older people.

But in natural English, be polite is the smoothest choice.