Från balkongen ser vi en regnbåge över sjön.

Because Swedish often puts a time, place, or other detail first when that is the starting point of the sentence.

Here, Från balkongen means from the balcony, and it has been moved to the front for emphasis or as the setting.

In Swedish main clauses, the finite verb usually comes in second position. This is often called the V2 rule.

So:

• Vi ser en regnbåge över sjön. = We see a rainbow over the lake.
• Från balkongen ser vi en regnbåge över sjön. = From the balcony, we see a rainbow over the lake.

Notice that when Från balkongen comes first, the verb ser must still stay in second position, so vi comes after the verb.

This is because of Swedish word order in main clauses.

When something other than the subject comes first, the verb still has to come second. So the subject moves after the verb.

Pattern:

• Subject + verb
  Vi ser ...
• Other element + verb + subject
  Från balkongen ser vi ...

This is very common in Swedish:

• Idag går jag till jobbet. = Today I’m going to work.
• På sommaren badar vi mycket. = In summer, we swim a lot.

So ser vi here is completely normal and required by standard Swedish grammar.

Från usually means from.

In this sentence, Från balkongen means that the balcony is the point or position from which we see the rainbow.

Some other examples:

• Jag kommer från Sverige. = I come from Sweden.
• Han tog boken från bordet. = He took the book from the table.
• Vi såg staden från tåget. = We saw the city from the train.

So here it gives the viewing location: from the balcony.

Balkongen is the definite form of en balkong.

• en balkong = a balcony
• balkongen = the balcony

Swedish usually puts the definite article at the end of the noun as a suffix.

Here, balkongen is definite because it refers to a specific balcony, probably one that is already known from the situation or context.

So:

• Från en balkong = from a balcony
• Från balkongen = from the balcony

The sentence uses the balcony, not just any balcony.

Because the sentence is talking about a rainbow, not the rainbow.

• en regnbåge = a rainbow
• regnbågen = the rainbow

Swedish uses en for common-gender nouns in the indefinite singular.

So the sentence presents the rainbow as something being seen, not necessarily something already identified beforehand.

Compare:

• Vi ser en regnbåge. = We see a rainbow.
• Vi ser regnbågen. = We see the rainbow.

Both are possible in other contexts, but here the indefinite form is the natural choice.

Sjön is the definite form of en sjö.

• en sjö = a lake
• sjön = the lake

The sentence says över sjön, meaning over the lake, so it is referring to a specific lake.

Again, Swedish usually marks definiteness by adding a suffix to the noun:

• en sjö
• sjö + n = sjön

So there is no separate word for the before the noun here. The -n ending already contains that meaning.

In this sentence, över sjön most naturally means over the lake in the sense of above the lake / in the sky above the lake.

That fits well with regnbåge (rainbow).

Över can sometimes mean different things depending on context, including:

• over / above
• across
• sometimes for in certain expressions

But here the meaning is clearly spatial: the rainbow is seen in the sky above the lake.

So över sjön is best understood as over the lake, not across the lake.

Yes. Ser is the present tense of the verb se, which means to see.

The verb is irregular:

• att se = to see
• ser = see / sees
• såg = saw
• sett = seen

Examples:

• Jag ser dig. = I see you.
• Vi ser en film. = We are watching a film / We see a film
  (depending on context)
• Hon såg en fågel. = She saw a bird.

So in the sentence, ser vi means we see.

Because Swedish usually attaches the definite article to the end of the noun.

This is one of the biggest differences from English.

Examples:

• en bok = a book
• boken = the book
• en stol = a chair
• stolen = the chair
• en sjö = a lake
• sjön = the lake

So in your sentence:

• balkongen = the balcony
• sjön = the lake

English uses a separate word (the), but Swedish often uses an ending instead.

All three nouns here are en-words (common gender):

• en balkong
• en regnbåge
• en sjö

That is why:

• the indefinite article is en
• the definite singular form often ends in -en or -n

So:

• en balkong → balkongen
• en regnbåge → regnbågen
• en sjö → sjön

This is useful to memorize with the noun, since Swedish nouns belong to either en gender or ett gender.

Yes, that is grammatically possible.

• Från balkongen ser vi en regnbåge över sjön.
• Vi ser en regnbåge över sjön från balkongen.

Both can mean essentially the same thing.

The difference is mostly about focus:

• Från balkongen ... puts the location first, as the setting.
• Vi ser ... från balkongen starts more neutrally with the subject.

Swedish often moves phrases like Från balkongen to the front when they set the scene or feel especially relevant.

Many learners find regnbåge a bit tricky because of the consonants and the vowel å.

A rough guide is:

• regn sounds roughly like rengn / rengn
• bå has the long å sound, somewhat like the vowel in British law
• ge here sounds like geh

A rough English-style approximation might be:

RENGN-boh-geh

But it is better to listen to native pronunciation if possible, because Swedish vowel length and stress matter a lot.

Also note:

• regn = rain
• båge = bow / arch

So regnbåge literally means rain-bow.

Yes. Från balkongen is a prepositional phrase, and in the sentence it functions as an adverbial of place or viewpoint.

It tells us from where the seeing happens.

The basic structure is:

• Från balkongen = adverbial
• ser = finite verb
• vi = subject
• en regnbåge = object
• över sjön = another adverbial phrase

So the sentence contains two location-related phrases:

• Från balkongen = where we are seeing from
• över sjön = where the rainbow is

That is a very typical Swedish sentence structure.