På den här gatan är trottoaren full av människor, så vi går två och två.

Because gata is a common-gender noun, and in this structure Swedish uses the definite form of the noun after den här.

So:

• en gata = a street
• gatan = the street
• den här gatan = this street

A very common pattern in Swedish is:

• den här + definite noun
• det här + definite noun
• de här + definite noun

Examples:

• den här boken = this book
• det här huset = this house
• de här skorna = these shoes

So den här gatan is the normal way to say this street.

Swedish normally says på en gata / på den här gatan for on a street.

So:

• på gatan = on the street
• på den här gatan = on this street

This is just the usual preposition with gata in this meaning. English learners sometimes expect i because it often means in, but for streets and roads Swedish very often uses på.

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

Here, the sentence starts with the adverbial phrase:

• På den här gatan = On this street

That takes the first position, so the verb must come next:

• På den här gatan är trottoaren full av människor

Compare:

• Trottoaren är full av människor på den här gatan
• På den här gatan är trottoaren full av människor

Both are possible, but when the sentence begins with På den här gatan, the verb moves before the subject.

Because the sentence is talking about the sidewalk on that particular street, so Swedish uses the definite form:

• en trottoar = a sidewalk
• trottoaren = the sidewalk

In context, it is natural to refer to the sidewalk as something specific and identifiable, so trottoaren fits well.

Literally, full av människor means full of people.

• full = full
• av = of
• människor = people / human beings

The adjective full normally takes av in Swedish:

• full av vatten = full of water
• full av idéer = full of ideas
• full av människor = full of people

So av is the standard preposition here.

Both can refer to people, but they are used a little differently.

• människor = people, human beings, individuals
• folk = people, folks, people in general, sometimes more collective

In this sentence, full av människor sounds very natural because it emphasizes that there are many individual people on the sidewalk.

You could hear full av folk too in everyday speech, and it would also sound natural, but människor is slightly more neutral and standard.

Here så means so, therefore, or as a result.

The sentence has two parts:

• På den här gatan är trottoaren full av människor
• så vi går två och två

So the idea is:

The sidewalk is full of people, so we walk two by two.

It connects the situation to the result.

Yes, gå can mean go, but it also very often means walk.

In this sentence, vi går is best understood as we walk, because the context is about moving along a crowded sidewalk.

Examples:

• Jag går till skolan. = I walk to school. / I go to school on foot.
• Vi går hem. = We walk home.
• Gå! = Go! / Walk!

So går here is a very natural choice.

Två och två means two by two, or more naturally in English, in pairs.

It describes how people are arranged while walking:

• en och en = one by one
• två och två = two by two / in pairs
• tre och tre = three by three / in groups of three

So vi går två och två means we walk in pairs.

Both are possible, but they are not always used in exactly the same way.

• två och två emphasizes the pattern: people are arranged two at a time
• i par means in pairs

In this sentence, två och två sounds very natural because it focuses on how the group is moving along the street. It gives a slightly more visual sense of the arrangement.

So:

• Vi går två och två = We walk two by two / in pairs
• Vi går i par = We walk in pairs

Both can work, but två och två is a very common expression.

Both mean this, but den här is more common in everyday spoken and written Swedish.

• den här gatan = this street
• denna gata = this street

Denna is correct, but it often sounds more formal, written, or official.

So in a normal everyday sentence, den här gatan is the most natural choice.

Yes, it is the same word historically and in form, but in den här gatan, it functions as part of the demonstrative expression meaning this.

Compare:

• Jag bor här. = I live here.
• den här gatan = this street

So här can be an adverb by itself, but after den/det/de it helps form expressions like:

• den här = this
• det här = this
• de här = these

Yes, that is also possible, but it means something slightly different:

• trottoaren är full av människor = the sidewalk is full of people
• trottoarerna är fulla av människor = the sidewalks are full of people

The original sentence uses the singular trottoaren, probably because it is referring to one sidewalk in the situation being described. If both sides of the street are meant, plural could be used.

Also notice the adjective agreement:

• trottoaren är full
• trottoarerna är fulla

A very literal version would be something like:

On this street is the sidewalk full of people, so we walk two and two.

That sounds awkward in English, but it helps show the Swedish structure.

A natural English version would be:

On this street, the sidewalk is full of people, so we walk in pairs.

This is a good example of how Swedish and English often express the same idea with slightly different word order and idioms.