Quiero comprar un melón y otro kiwi en la frutería para esta tarde.

Because otro normally replaces the indefinite article in Spanish. You say:

• un melón = a melon
• otro kiwi = another kiwi

Not un otro kiwi.

This is a very common pattern:

• Quiero un café y otro té.
• Compré una manzana y otra pera.

So otro already carries the idea of another / one more, and you do not add un before it.

Because the first fruit is being introduced simply as a melon, so Spanish uses the indefinite article un.

The second fruit is presented as another / one more item, so Spanish uses otro instead of un.

So the structure is:

• un melón = a melon
• otro kiwi = another kiwi / one more kiwi

It does not necessarily mean there was already a kiwi mentioned earlier in the sentence in English-style logic. In Spanish, otro can simply mean an additional one.

In Spanish, nouns have grammatical gender, and kiwi is usually treated as masculine when it refers to the fruit:

• un kiwi
• otro kiwi

There is no obvious ending like -o or -a to help, so this is something learners usually just memorize.

If you are talking about the fruit shop context, kiwi here clearly means the fruit, not a person from New Zealand.

Quiero comprar literally means I want to buy.

• quiero = I want
• comprar = to buy

In everyday use, it can sound a bit softer than the English I want, depending on context. In a shop, Spaniards often also say things like:

• Quería... = I wanted... / I’d like...
• Me pone... = Can I have... / Please give me...

But Quiero comprar is grammatically correct and completely understandable.

Because after querer meaning to want, Spanish normally uses an infinitive for the next verb.

Pattern:

• querer + infinitive

Examples:

• Quiero comer = I want to eat
• Quiero ir = I want to go
• Quiero comprar = I want to buy

This is similar to English want to buy, except Spanish does not need a separate word equivalent to to before the second verb in the same way English does.

Because en here means at / in the fruit shop, describing the place where the buying happens.

• en la frutería = at the greengrocer’s / in the fruit shop

If you said a la frutería, that would usually suggest movement to the shop:

• Voy a la frutería = I’m going to the fruit shop

So:

• comprar ... en la frutería = buy ... at the fruit shop
• ir a la frutería = go to the fruit shop

A frutería is a shop that sells fruit, and often vegetables too. In English, depending on context, you might translate it as:

• fruit shop
• greengrocer’s
• produce shop

In Spain, this is a very common everyday word.

Because para here expresses purpose or intended use/time: the fruit is being bought for this afternoon / for later today.

• para esta tarde = for this afternoon / for later today

In contrast, por would usually express things like cause, movement through, exchange, or approximate time, and it would not sound natural here.

So this sentence is using para to show what the purchase is intended for.

In Spain, esta tarde usually refers broadly to the later part of the day after lunch, so it often covers what English might call this afternoon, and sometimes part of what English speakers might think of as this evening.

Depending on context, a natural translation could be:

• for this afternoon
• for later today
• sometimes for this evening

If you want to be very specifically tonight, Spanish usually uses esta noche.

Because demonstratives like este, esta, estos, estas already work like determiners before a noun, so you do not normally add an article before them.

• esta tarde = this afternoon
• este melón = this melon

Not:

• la esta tarde
• el este melón

This is similar to English: you say this afternoon, not the this afternoon.

The given word order is natural:

• Quiero comprar un melón y otro kiwi en la frutería para esta tarde.

But Spanish word order is somewhat flexible, especially with prepositional phrases. For example, you could also hear:

• Quiero comprar en la frutería un melón y otro kiwi para esta tarde.

That said, the original version is clearer and more neutral for a learner.

A very common pattern is:

• verb + objects + place + time/purpose

So the sentence sounds normal as it is.

Yes. In this context, otro kiwi most naturally means another kiwi or simply one more kiwi.

If you want to think of it practically, the speaker wants two items:

• un melón
• otro kiwi

So in natural English, this could be:

• a melon and another kiwi
• or just a melon and a kiwi, if the broader context does not matter

Spanish often uses otro where English might or might not make another explicit.

Y means and.

It changes to e before words that begin with an i sound:

• padre e hijo
• España e Italia

But here the next word is otro, so it stays y:

• un melón y otro kiwi

So the rule depends on the sound of the following word, not just the general structure of the sentence.