Rahma alihesabu silabi za neno hilo tena na akasema herufi ya mwisho si konsonanti, bali irabu.

Alihesabu can be broken down like this:

• a- = 3rd person singular subject marker, he/she
• -li- = past tense
• -hesabu = verb root from kuhesabu, to count

So alihesabu means he/she counted.

Swahili verbs do not show gender, so a- can mean either he or she. The name Rahma tells you who the subject is, and the English translation chooses she from the context.

Many Swahili loanwords, especially in noun classes 9/10, have the same form in both singular and plural.

So:

• silabi can mean syllable
• silabi can also mean syllables

You tell the difference from context and agreement words around it. In this sentence, za shows that silabi is plural, so it means syllables.

Because silabi is plural here.

The connector -a changes form to agree with the noun before it:

• singular class 9 often takes ya
• plural class 10 takes za

So:

• silabi ya neno hilo = the syllable of that word
• silabi za neno hilo = the syllables of that word

Even though silabi looks the same in singular and plural, the agreement word za tells you this one is plural.

In normal Swahili word order, demonstratives usually come after the noun.

So:

• neno hilo = that word
• literally, something like word that

Also, hilo agrees with neno, which is a class 5 noun. Swahili demonstratives change form to match the noun class, so you cannot use just one fixed word for that with every noun.

Here tena means again.

So alihesabu ... tena means she counted them one more time, or repeated the counting.

In other contexts, tena can sometimes have slightly different shades such as further, also, or then again, but in this sentence again is the natural meaning.

This is a very common Swahili storytelling or sequence pattern.

• alisema = he/she said
• akasema = and then he/she said / so he/she said

The -ka- tense marker often shows the next action in a sequence after an earlier action. So:

• Rahma alihesabu ... na akasema ...

means she first counted, and then after that she spoke.

Using akasema makes the flow of events feel more connected and natural.

Because they do slightly different jobs.

• na links the two clauses: and
• aka- marks the second action as the next event in the sequence

So na akasema is not redundant. It is a very natural way to say and then she said.

Herufi ya mwisho literally means letter of the end, but idiomatically it means the last letter or the final letter.

Parts:

• herufi = letter
• ya = linking word, agreeing with herufi
• mwisho = end

This pattern is common in Swahili:

• siku ya mwisho = the last day
• ukurasa wa mwisho = the last page
• herufi ya mwisho = the last letter

Si is the negative form used when identifying or classifying something.

So:

• ni konsonanti = it is a consonant
• si konsonanti = it is not a consonant

In this sentence, the speaker is saying what kind of thing the final letter is not. That is why si is used.

You may also see siyo or sio, but before a noun like this, si is the basic and very common form.

Bali means but rather or but instead.

It is especially common after a negative statement when you correct it:

• si konsonanti, bali irabu
• not a consonant, but rather a vowel

This is more specific than lakini, which is the general word for but.

So:

• lakini = general contrast
• bali = correction/replacement after a negative idea

That makes bali exactly right here.

Swahili does not have articles like English a, an, and the.

So nouns often appear by themselves, and English adds the article when translating:

• konsonanti → a consonant
• irabu → a vowel

Whether something is definite or indefinite usually comes from context, not from a separate article word. In this sentence, English naturally says not a consonant, but a vowel, even though Swahili does not use words matching a.

Yes. It is a very common contrast pattern in Swahili:

• si X, bali Y = not X, but Y

For example:

• si chai, bali kahawa = not tea, but coffee
• si leo, bali kesho = not today, but tomorrow

So in your sentence:

• si konsonanti, bali irabu

is a neat, standard way to correct the first classification and replace it with the right one.