I förrgår köpte jag två äpplen och två päron på marknaden.

No. In this sentence, I is just the first word of the Swedish expression i förrgår, and it is capitalized only because it starts the sentence.

So:

• i förrgår = the day before yesterday
• i here is not the English pronoun I

If the phrase came later in the sentence, it would be lowercase:

Jag köpte två äpplen och två päron i förrgår.

I förrgår means the day before yesterday.

Useful comparison:

• i dag = today
• i går / igår = yesterday
• i förrgår = the day before yesterday
• i morgon / imorgon = tomorrow

You usually learn i förrgår as a fixed time expression.

This is because Swedish follows the V2 rule in main clauses. V2 means the finite verb normally comes in the second position.

Here, the sentence begins with the time expression I förrgår. That takes the first position, so the verb köpte has to come next:

• I förrgår = position 1
• köpte = position 2
• jag = after the verb

So:

• I förrgår köpte jag ... = correct
• I förrgår jag köpte ... = incorrect

Yes. That is also correct.

The difference is mainly about focus:

• I förrgår köpte jag ... puts the time first and gives it emphasis
• Jag köpte ... i förrgår starts with the subject and sounds a bit more neutral

Both are natural Swedish.

In Swedish, when you use a number like två, you normally use the noun without an article:

• två äpplen = two apples
• två päron = two pears

This is similar to English, where you also say two apples, not two the apples or two some apples.

Because Swedish nouns form their plurals in different ways.

Here you have:

• ett äpple → två äpplen
• ett päron → två päron

So:

• äpple gets the plural ending -n
• päron has the same form in singular and plural indefinite

This is normal in Swedish. Nouns belong to different plural patterns, so you often have to learn the plural together with the singular.

Because Swedish normally says på marknaden for at the market.

This is the usual preposition for being at a market as a place or event.

Compare:

• på marknaden = at the market
• till marknaden = to the market
• i marknaden would usually not be the normal choice here

So in this sentence, the buying happened at the market, which is why på is used.

Because marknaden is the definite singular form of marknad.

Swedish usually adds the definite article as an ending:

• en marknad = a market
• marknaden = the market

So på marknaden means at the market.

That is just how Swedish usually forms the definite article.

English uses a separate word:

• the market

Swedish usually attaches it to the noun:

• marknaden

More examples:

• en bok = a book
• boken = the book
• ett äpple = an apple
• äpplet = the apple

This is one of the basic structural differences between English and Swedish.

Normally, no.

Swedish does not usually put a comma after a short introductory time expression like this. So the normal punctuation is:

I förrgår köpte jag två äpplen och två päron på marknaden.

In careful speech, jag is pronounced roughly like yag.

In everyday spoken Swedish, it is very often reduced and can sound more like:

• ya
• ja with a y sound at the start

So in natural speech, köpte jag may sound a bit like shop-te ya in rough English approximation.

A rough English-style approximation is:

ee FURR-gor SHOP-te ya tvoh EP-len å tvoh PEH-ron po MARK-na-den

A few notes:

• kö in köpte has the Swedish ö sound, which English does not have exactly
• och is often pronounced more like å in normal speech
• jag is often reduced to ya
• äpplen has two syllables: ÄPP-len

This is only an approximation, but it can help you get started.