Msikiti uko karibu na soko la mjini.

Because uko is the form used for location: it means something like is located or is there.

So in this sentence:

• Msikiti uko ... = The mosque is located ...

By contrast, ni is usually used to identify or classify something:

• Msikiti ni jengo = The mosque is a building

So for where something is, uko is the natural choice.

Msikiti is normally treated as a class 3 singular noun in Swahili. That matters because noun class affects agreement.

Here, the location word uko contains the agreement prefix u-, which matches msikiti.

A useful comparison:

• singular: msikiti uko ...
• plural: misikiti iko ...

So the form of the verb-like element changes to match the noun class.

Karibu na means near or close to.

Examples:

• karibu na soko = near the market
• karibu na nyumba = near the house

So in your sentence, uko karibu na ... means is near ...

Yes. It is the same word, but the meaning changes with context.

Karibu has a basic idea of nearness or coming close, so it can be used in different ways:

• Karibu! = Welcome!
• karibu na = near / close to

So in Msikiti uko karibu na soko la mjini, it clearly means near, not welcome.

No. Here na is part of the phrase karibu na, meaning near to.

It is true that na often means and, but it has several uses in Swahili. In this sentence, it is not joining two nouns the way and would. It belongs to the expression karibu na.

So:

• Juma na Asha = Juma and Asha
• karibu na soko = near the market

The word la is the associative linker. It connects soko with mjini.

• soko = market
• la = linker agreeing with soko
• mjini = in town / town area

So soko la mjini is literally something like the market of the town / the market in town, and more naturally the town market or the market in town.

The reason it is la specifically is that soko belongs to noun class 5, and class 5 uses la in this kind of construction.

Mji means town or city.

Mjini is the locative form, meaning in town, in the town, or sometimes downtown / urban area, depending on context.

The ending -ni is a common locative ending in Swahili. So:

• mji = town
• mjini = in town

That is why soko la mjini suggests the market in town or the town market, not just market of town in a mechanical word-for-word sense.

Because Swahili usually does not use articles like a, an, or the.

So a noun like msikiti can mean:

• a mosque
• the mosque

And soko can mean:

• a market
• the market

The exact meaning depends on context. English requires articles, but Swahili normally does not.

Yes, the order here is the normal, natural one:

• Msikiti = subject
• uko = is located
• karibu na soko la mjini = near the town market

So the full pattern is:

Subject + location form + place phrase

You can sometimes change word order for emphasis, but the version you were given is the standard and most useful one to learn first.

A simple pronunciation guide is:

• Msikiti = m-see-KEE-tee
• uko = oo-KOH
• karibu na = kah-REE-boo nah
• soko la mjini = SOH-koh lah m-JEE-nee

A few useful pronunciation notes:

• Swahili vowels are usually very consistent:
  • a as in father
  • e as in bed but cleaner
  • i as in machine
  • o as in told but shorter
  • u as in flute
• Stress usually falls on the second-to-last syllable:
  • msiKIti
  • uKO
  • kariBU
  • SOko
  • mJIni

So the whole sentence flows quite regularly once you know the syllables.