Learn Hardcore Swahili: Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo? - You have been reading many more books this year, haven’t you?

Together, umekuwa ukisoma corresponds closely to English you have been reading, that is, an action or habit that has been going on for some time up to the present (similar to the English present perfect continuous).

Why do we need both umekuwa and ukisoma? Would umesoma vitabu vingi zaidi mwaka huu mean the same thing?

They are not the same.

umesoma vitabu vingi zaidi mwaka huu
- umesoma = you have read (simple perfect, completed action)
- This focuses on the fact that, in total, you have read many more books this year.
umekuwa ukisoma vitabu vingi zaidi mwaka huu
- umekuwa ukisoma = you have been reading
- This emphasizes an ongoing pattern or habit over this year. It is more like saying you’ve been in the habit of reading more books this year.

So:

umesoma: result / completed achievement.
umekuwa ukisoma: process / ongoing behavior over a period.

Is wewe necessary here, or could I just say Umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?

wewe is not grammatically necessary, because the subject you is already expressed by the prefix u- on the verb (umekuwa, ukisoma).

Without wewe: Umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?
- Correct, natural, fairly neutral.
With wewe: Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?
- Adds emphasis or contrast: You have been reading more books this year (implied: not someone else).

So wewe is optional and mainly used for emphasis, contrast, or clarity.

How does the tag sivyo? work, and how does it compare to English tags like …haven’t you?

sivyo is made of:

si – not
ivyo – like that / so

So sivyo? literally means is it not so? / isn’t that right?

Function:

It is a general tag question asking for confirmation, similar to English right? / isn’t that so? / isn’t it?
It does not change according to the tense or subject like English tags do. You can attach sivyo? to a wide variety of statements.

Example:

Umechoka, sivyo? – You’re tired, right?
Unaishi Dar es Salaam, sivyo? – You live in Dar es Salaam, right?

In your sentence, …, sivyo? roughly matches …haven’t you? in function, but the grammar is much simpler.

Can I use siyo? instead of sivyo? in this sentence?

Yes. These are common variants:

Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?
Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, siyo?

Both sound natural.

Nuance:

sivyo? – a bit more neutral / standard.
siyo? – slightly more colloquial or conversational.

The basic meaning in this context is the same: asking for confirmation.

I thought -ki- usually meant when/if (as in ukisoma = when you read). Why is ukisoma here understood as reading?

You are right that -ki- often means when/if:

Ukisoma, utafaulu. – When/If you study, you will pass.

But in the special pattern [kuwa] + [ki- + verb], -ki- marks a progressive / ongoing action, not a conditional.

Examples:

Nimekuwa nikifanya kazi nyingi.
= I have been doing a lot of work.
Amekuwa akisafiri sana.
= He/She has been traveling a lot.
Umekuwa ukisoma vitabu vingi zaidi.
= You have been reading many more books.

So, with umekuwa ukisoma, the meaning is you have been reading, not if/when you read. The presence of umekuwa strongly pushes ukisoma into this progressive meaning.

What is the difference between umekuwa ukisoma and just unasoma in a sentence like this?

Compare:

Mwaka huu unasoma vitabu vingi zaidi.
– This year you read / are reading more books.
(Present / present habitual: focuses on the current pattern, but not explicitly on its duration.)
Mwaka huu umekuwa ukisoma vitabu vingi zaidi.
– This year you have been reading many more books.
(Present perfect continuous: emphasizes that this has been the pattern over some time up to now, often with a sense of change compared to before.)

So umekuwa ukisoma adds a feeling of:

duration (over a period), and
sometimes change (this is a new or noticeable trend).

Why do we say vitabu vingi zaidi? How do vitabu, vingi, and zaidi each contribute to the meaning?

Breakdown:

vitabu – books (noun, class 8 plural)
vingi – many (adjective agreeing with class 8)
zaidi – more / in a greater amount / extra

So vitabu vingi zaidi → many more books / a lot more books.

vitabu vingi alone = many books.
Adding zaidi: vitabu vingi zaidi = even more books than before / a larger quantity than some reference point.

The typical order for this meaning is Noun + Adjective + zaidi.

Could I say just vitabu zaidi instead of vitabu vingi zaidi?

Yes, you can, but you will lose a bit of the emphasis.

vitabu zaidi = more books (comparative, but neutral about whether the number is large).
vitabu vingi zaidi = many more books / a lot more books, emphasizing both:
- that they are many (vingi), and
- that this is more than before (zaidi).

Your original sentence with vitabu vingi zaidi sounds stronger, like stressing in English: You’ve been reading a lot more books this year, haven’t you?

Why is the adjective vingi used with vitabu? Could it be mengi instead?

Swahili adjectives must agree with the noun class.

kitabu (book) – class 7
vitabu (books) – class 8

The adjective -ingi (many, much) changes form depending on the class:

class 7: kikubwa, kimoja, etc., but for many we say kingi (rare with countables)
class 8: vingi
class 6 (e.g. maji, maziwa): mengi

So:

vitabu vingi – many books (correct)
vitabu mengi – incorrect, because mengi agrees with class 6, not class 8.

That is why vingi is used with vitabu.

How does mwaka huu work grammatically, and is huyu mwaka also correct?

mwaka (year) belongs to noun class 3.
The class 3 demonstrative this is huu.

So:

mwaka huu = this year (standard, grammatically correct).

Many native speakers in everyday speech say huyu mwaka, using huyu (the class 1 human demonstrative) by analogy, but for learners it is better to stick to the standard:

mwaka huu – recommended, standard form.
huyu mwaka – widely heard colloquially, but not standard grammar.

Can the phrase mwaka huu move to a different position in the sentence, and does that change the meaning?

Yes, mwaka huu is a time expression and is quite flexible in position. All of these are grammatically correct:

Mwaka huu, wewe umekuwa ukisoma vitabu vingi zaidi, sivyo?
Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?
Umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo?

The basic meaning is the same: This year you have been reading many more books, haven’t you?

The difference is mainly in emphasis:

At the beginning (Mwaka huu, …) → emphasizes the time frame, this year as the topic.
Right before sivyo? (as in the original) → feels neutral; time is specified but focus is on you and your behavior.

Is the whole sentence Wewe umekuwa ukisoma vitabu vingi zaidi mwaka huu, sivyo? formal, informal, or neutral? Would it sound natural in everyday conversation?

It is natural and roughly neutral:

The structure umekuwa ukisoma is typical standard Swahili for have been reading.
The tag sivyo? is slightly on the careful/standard side but still common in speech.

In very casual conversation, speakers might say, for example:

Mwaka huu unasoma vitabu vingi zaidi, siyo?

But your original sentence is completely idiomatic and can be used in everyday conversation without sounding strange.