Agosti mwaka jana tulikaa nyumbani, lakini Septemba tulianza safari ndefu.

In Swahili, month names can often be used on their own as time expressions, without a separate word for in.

So:

• Agosti mwaka jana = last August
• Septemba = in September / September

This is very natural in Swahili. You do not need to add a preposition like English in before the month.

Mwaka jana means last year.

• mwaka = year
• jana = yesterday, but in the expression mwaka jana, it means last

This is a very common pattern in Swahili:

• mwaka jana = last year
• wiki jana = last week
• mwezi jana = last month

So Agosti mwaka jana means August of last year or more naturally last August.

That is a good question because jana does indeed often mean yesterday.

But in some time expressions, jana extends to the idea of the previous one:

• jana alone = yesterday
• mwaka jana = last year
• wiki jana = last week
• mwezi jana = last month

So the exact meaning depends on the phrase it appears in.

Tulikaa breaks down like this:

• tu- = we
• -li- = past tense marker
• kaa = verb root meaning stay, live, remain

So:

• tu-li-kaa = we stayed

The same pattern appears in many verbs:

• tulisoma = we read / we studied
• tuliona = we saw
• tulianza = we began

Not in this sentence.

The verb kaa can have meanings like stay, remain, live, or sometimes sit, depending on context. Here, in tulikaa nyumbani, it means we stayed at home.

So this is not really we sat at home, but rather we remained / stayed at home.

Nyumbani means at home or home. It is a very common locative form.

• nyumba = house / home
• nyumbani = at home / in the house / home

In many situations, Swahili uses this -ni locative ending to express place.

Examples:

• shuleni = at school
• sokoni = at the market
• nyumbani = at home

So tulikaa nyumbani is the natural way to say we stayed at home.

Tulianza breaks down like this:

• tu- = we
• -li- = past tense
• anza = begin / start

So:

• tu-li-anza = we began / we started

This is the same subject + tense pattern as tulikaa.

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

So:

• safari ndefu can mean a long journey, the long journey, or just long journey, depending on context.

You have to understand definiteness from the situation, not from an article.

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

So:

• safari ndefu = journey long = long journey

This is the normal word order.

Other examples:

• mtu mzuri = good person
• nyumba kubwa = big house
• kitabu kipya = new book

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

Safari belongs to the N-class, and many adjectives with N-class nouns either stay the same or take an n- form. That is why we get:

• safari ndefu = long journey

You can compare:

• nyumba ndefu = tall/long house
• barabara ndefu = long road

So ndefu is the agreeing form used with this noun class.

Lakini means but.

It connects the two parts of the sentence:

• Agosti mwaka jana tulikaa nyumbani = Last August we stayed at home
• lakini Septemba tulianza safari ndefu = but in September we began a long journey

So it works very much like English but.

Swahili often places time expressions near the beginning of the sentence or clause, especially when setting the scene.

So:

• Agosti mwaka jana tulikaa nyumbani
• Septemba tulianza safari ndefu

This structure highlights when the action happened. It is very natural in Swahili.

You could think of it as:

• Last August, we stayed at home, but in September, we began a long journey.

Yes, you can.

• Agosti = August
• mwezi wa Agosti = the month of August

Both are correct, but Agosti by itself is very common and more concise.

So this sentence could be expanded, but it would sound less compact:

• Mwezi wa Agosti mwaka jana tulikaa nyumbani...

The original version is perfectly natural.

Safari is a broad word. It can mean:

• trip
• journey
• travel

So safari ndefu can be understood as:

• a long journey
• a long trip

The exact English choice depends on context. In this sentence, either one works well.