Sokoni tulinunua tikitimaji kubwa, papai moja, na zabibu kwa ajili ya wageni.

Sokoni comes from soko (market) plus the locative ending -ni.

So sokoni means at the market, in the market, or sometimes to the market, depending on context.
In this sentence, because the verb is we bought, the natural meaning is at the market.

This -ni ending is very common in Swahili for places:

• shule → shuleni = at school
• nyumba → nyumbani = at home
• soko → sokoni = at the market

Tulinunua contains several pieces:

• tu- = we
• -li- = past tense
• -nunua = buy

So tulinunua literally means we-bought.

This is normal in Swahili: the subject is usually built into the verb, so you often do not need a separate pronoun like sisi (we).
If you added sisi, it would usually be for emphasis:

• Sisi tulinunua... = We bought... / It was we who bought...

Swahili normally does not use articles like English a/an/the.

So:

• tikitimaji kubwa can mean a big watermelon or the big watermelon
• papai moja can mean one papaya
• wageni can mean guests or the guests

Context tells you which meaning is intended. This is very common in Swahili, so learners need to get used to relying more on context than on articles.

In Swahili, adjectives usually come after the noun they describe.

So:

• tikitimaji kubwa = big watermelon
• literally: watermelon big

This is the normal word order for many noun modifiers in Swahili:

• mtoto mdogo = small child
• nyumba kubwa = big house
• kitabu kizuri = good book

So tikitimaji kubwa follows the standard pattern.

Swahili adjectives usually agree with the noun class of the noun they describe.

Tikitimaji is a singular noun in the ji-/ma- class (class 5 in the singular). With the adjective stem -kubwa, the class 5 singular form is simply kubwa.

So:

• tikitimaji kubwa = big watermelon
• plural: matikitimaji makubwa = big watermelons

A useful point for learners: some agreement forms are very visible, while others look less different. Here, kubwa is the correct agreeing form.

Like adjectives, numbers usually come after the noun in Swahili.

So:

• papai moja = one papaya
• literally: papaya one

This is the normal pattern:

• kitabu kimoja = one book
• ndizi mbili = two bananas
• watoto watatu = three children

So the noun-first order is expected.

Moja means one, and here it agrees correctly with papai.

Papai is a singular noun, so moja is the right form for one papaya:

• papai moja

If it were plural, the noun and number would change:

• mapapai mawili = two papayas

So this phrase shows both meaning and agreement at the same time.

Here zabibu means grapes.

It belongs to a noun class where singular and plural often have the same form, so context tells you whether it is singular or plural.

That means:

• zabibu can refer to a grape or grapes, depending on context
• if you want to make the number clear, you can add a number or adjective:
  • zabibu moja = one grape
  • zabibu nyingi = many grapes

In this sentence, because it is part of a shopping list and the meaning is already given, it is understood as grapes.

Kwa ajili ya is a very common expression meaning:

• for
• for the sake of
• intended for

So:

• kwa ajili ya wageni = for the guests

It is best learned as a whole chunk.
In this sentence, it tells you the purpose of the purchase: the items were bought for the guests.

In normal reading, it applies to the whole shopping list, not just zabibu.

So the sense is:

• We bought a big watermelon, one papaya, and grapes, all for the guests.

Because the phrase comes at the end of the sentence, it naturally refers to the overall action or the whole set of items.

If a speaker wanted to make it clear that only the grapes were for the guests, they would usually rephrase the sentence.

Because wageni is plural.

• mgeni = guest
• wageni = guests

This is a very common pattern for nouns referring to people:

• mtoto / watoto = child / children
• mwalimu / walimu = teacher / teachers
• mgeni / wageni = guest / guests

Since the meaning is plural, wageni is the correct form.

The sentence does not have to start with Sokoni.

You could also say:

• Tulinunua tikitimaji kubwa, papai moja, na zabibu sokoni kwa ajili ya wageni.

That would still be understandable.

Starting with Sokoni puts the location first and gives it a little more emphasis, something like:

• At the market, we bought...

Swahili word order is somewhat flexible, especially with time and place expressions, but the basic order inside noun phrases usually stays the same:

• noun before adjective
• noun before number

So tikitimaji kubwa and papai moja would normally not be rearranged.