В магазине мы купили манго и киви для завтрака.

Because в магазине means in/at the store as a location, and after в when you are talking about location, Russian usually uses the prepositional case.

• магазин = store
• в магазине = in the store / at the store

Compare:

• в магазин = to the store (direction, motion)
• в магазине = in the store (location)

So in this sentence, the buying happened there, so в магазине is correct.

It is the prepositional case.

The noun магазин changes like this:

• nominative: магазин
• prepositional: в магазине

This is a very common pattern for masculine nouns after в or на when they describe location.

Russian often can drop subject pronouns when the verb already makes the subject clear. So Купили манго и киви... could work in the right context.

But мы is still perfectly normal to include. It can:

• make the sentence clearer,
• add slight emphasis to we,
• sound natural when starting a new statement.

So both are possible:

• Мы купили манго и киви...
• Купили манго и киви...

The version with мы is just a bit more explicit.

Купили is the past tense plural form of купить.

• купить = to buy
• купил = he bought
• купила = she bought
• купило = it bought
• купили = they bought / we bought / you (plural/formal) bought

Russian past tense agrees with the subject in gender and number, not person. Since the subject is мы (we), the plural form купили is used.

Also, купить is perfective, so купили means they/we bought in the sense of a completed action.

Because this sentence describes a completed purchase: we went and bought the fruit. In Russian, that usually calls for the perfective verb купить.

• купить = to buy, complete the purchase
• покупать = to be buying / to buy regularly / process of buying

So:

• Мы купили манго и киви. = We bought mango and kiwi.
• Мы покупали манго и киви. = We were buying / used to buy / bought on some occasion with focus on process or repeated action.

In your sentence, the completed event is the main idea, so купили is the natural choice.

Because манго and киви are usually treated as indeclinable nouns in Russian. That means their form stays the same in different cases.

Here they are direct objects, but they still remain:

• манго
• киви

This is common with some borrowed words in Russian.

So even though many Russian nouns would change form as objects, these two normally do not.

They function as direct objects, so grammatically they are in the accusative case.

However, because these nouns are indeclinable, their accusative form looks exactly the same as the dictionary form.

So the case is still accusative in function, even though there is no visible ending change.

Because the preposition для always requires the genitive case.

• завтрак = breakfast
• для завтрака = for breakfast

So завтрак changes to завтрака because it is after для.

This is a very important pattern to remember:

• для мамы = for mom
• для друга = for a friend
• для завтрака = for breakfast

It means for breakfast, in the general English sense.

Russian does not have articles like a/an/the, so whether English translation uses a or the depends on context.

So для завтрака simply means something like:

• for breakfast
• for the breakfast meal

In most natural English translations, for breakfast is best.

Not by itself. Для завтрака just means for breakfast.

If you wanted to say for tomorrow’s breakfast, Russian would usually make that explicit, for example:

• для завтрашнего завтрака = for tomorrow’s breakfast

So in your sentence, для завтрака is general: the mango and kiwi were bought for breakfast, with no specific day stated.

Yes, Russian word order is flexible. This version puts В магазине first to set the scene: in the store / at the store.

Other possible orders include:

• Мы купили манго и киви в магазине для завтрака.
• Манго и киви мы купили в магазине для завтрака.

The basic meaning stays similar, but the emphasis changes.

In В магазине мы купили манго и киви для завтрака, the speaker starts with the place, almost like: As for the store, that’s where we bought the mango and kiwi for breakfast.

It can mean either, depending on how natural English would express it.

Russian в магазине literally means in the store, but in English we often say at the store. So both can be good translations depending on context.

For this sentence, natural English could be:

• At the store, we bought mango and kiwi for breakfast.
• In the store, we bought mango and kiwi for breakfast.

Usually at the store sounds more natural in English.

Because Russian has no articles.

English needs words like:

• a
• an
• the

Russian does not use them. The listener understands from context whether something is general or specific.

So:

• в магазине can mean in a store or in the store
• манго и киви can mean mango and kiwi, some mango and kiwi, or the mango and kiwi, depending on context

That is completely normal in Russian.

They are two separate nouns joined by и (and), so together they refer to two items/types of fruit.

Each word itself is singular in form:

• манго = mango
• киви = kiwi

But together, манго и киви means mango and kiwi as a pair/list.

In English, depending on context, this could mean:

• one mango and one kiwi,
• some mango and some kiwi,
• mango and kiwi as food items.

Russian leaves that a bit open unless the context or a number makes it specific.

Yes, in English that may be a natural translation depending on context.

Russian often does not specify count as clearly as English in short sentences like this, especially with fruit names. So манго и киви could refer to the fruit in a general way.

If the speaker wanted to be very specific about number, Russian could add numerals, for example:

• одно манго и два киви = one mango and two kiwis

Without numbers, the exact quantity is not the main point.

The usual stress is:

• в магази́не
• мы купи́ли
• ма́нго
• ки́ви
• для за́втрака

Stress is important in Russian pronunciation, because it is not always predictable from spelling.