Nilisoma karibu asilimia hamsini ya kitabu jana usiku.

Nilisoma already includes I inside the verb.

It breaks down like this:

• ni- = I
• -li- = past tense
• -soma = read / study

So nilisoma means I read or I studied.

In Swahili, the subject is often built into the verb, so you usually do not need a separate pronoun like mimi unless you want emphasis.

It can mean both.

• kusoma kitabu = to read a book
• kusoma kwa mtihani = to study for an exam

In this sentence, because the object is kitabu (book), the natural meaning is read.

Here, karibu means almost, nearly, or sometimes about/approximately, depending on context.

So karibu asilimia hamsini means something like:

• almost fifty percent
• nearly fifty percent
• sometimes about fifty percent

This is different from other common meanings of karibu, such as near or welcome.

Asilimia means percent, and hamsini means fifty.

So:

• asilimia hamsini = fifty percent

This is the normal order in Swahili: the word for percent comes first, then the number.

Because ya means of, and it agrees with asilimia, not with kitabu.

So the structure is:

• asilimia hamsini ya kitabu
• literally: fifty percent of the book

A learner might expect agreement with kitabu, but the head of the phrase is asilimia. That is why ya is used here.

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

So kitabu can mean:

• a book
• the book

The exact meaning depends on context. In this sentence, the context makes it clear that the book is meant.

Jana means yesterday, and usiku means night.

Together, jana usiku is the normal way to say last night.

So even though the words are literally yesterday night, the natural English meaning is last night.

Yes, it can move.

Swahili word order is fairly flexible, especially for time expressions. The sentence can also be:

• Jana usiku nilisoma karibu asilimia hamsini ya kitabu.

That means the same thing: Last night, I read nearly fifty percent of the book.

Putting the time expression at the end is completely natural.

Nilisoma is simple past: I read.

It usually presents the action as a completed event. In this sentence, that fits well because the speaker is talking about how much of the book was read.

If you wanted to emphasize an ongoing action, Swahili would often use a different form, for example:

• nilikuwa nasoma = I was reading

So nilisoma is the better choice here.

Yes.

• nusu ya kitabu = half of the book
• asilimia hamsini ya kitabu = fifty percent of the book

They are very close in meaning, but nusu sounds more natural in everyday speech when you simply mean half.
Asilimia hamsini sounds a bit more numerical or precise.

So you could also say:

• Nilisoma karibu nusu ya kitabu jana usiku.

That would mean I read almost half of the book last night.