Kan du skicka in blanketten så snabbt som möjligt?

Because Swedish forms yes/no questions by putting the finite verb first.

• Statement: Du kan skicka in blanketten. = You can send in the form.
• Question/request: Kan du skicka in blanketten? = Can you send in the form?

In this sentence, Kan du ... ? is not only about ability. Just like in English, it is also a very common way to make a polite request: Can you ... ?

It is usually polite and completely normal in everyday Swedish.

Swedish generally uses fairly direct wording compared with English, so Kan du skicka in blanketten ... ? sounds natural, not rude.

If you want to sound a bit softer or more formal, you could say:

• Skulle du kunna skicka in blanketten ... ? = Could you send in the form ... ?

But the original sentence is already standard and polite.

Skicka in is a verb + particle combination meaning send in or submit.

So:

• skicka = send
• skicka in = send in / submit

In this sentence, it means sending the form to an office, organization, website, or authority.

Without in, skicka would just mean send, which is more general.

Because skicka in is a particle verb, and in Swedish these are often written as two words.

In the infinitive, you usually say:

• att skicka in

In a main clause:

• Jag skickar in blanketten.
• Kan du skicka in blanketten?

So the separate in is normal here.

Blanketten means the form.

The basic word is:

• en blankett = a form

The definite form is:

• blanketten = the form

Swedish usually adds the definite ending to the noun itself instead of putting a separate word like the in front.

So:

• en blankett = a form
• blanketten = the form

Because Swedish often puts definiteness at the end of the noun.

English says:

• the form

Swedish says:

• blanketten

That final -en already contains the meaning of the.

Because snabbt is the adverb form, and here it describes how the action should be done.

• snabb = quick / fast as an adjective
• snabbt = quickly / fast as an adverb

Examples:

• en snabb bil = a fast car
• köra snabbt = drive fast

In så snabbt som möjligt, the word modifies the action of submitting, so the adverb snabbt is needed.

It means as quickly as possible.

This is a very common Swedish pattern:

• så + adjective/adverb + som möjligt

So:

• så snabbt som möjligt = as quickly as possible
• så snart som möjligt = as soon as possible
• så ofta som möjligt = as often as possible

Literally, it is something like so quickly as possible, but in natural English we translate it as as quickly as possible.

Yes. In many situations, så snart som möjligt is even more common.

The difference is small:

• så snabbt som möjligt focuses on doing it quickly
• så snart som möjligt focuses on doing it at the earliest possible time

In this sentence, both would sound natural.

The particle in adds the idea of sending something in to an authority, office, or system.

• skicka blanketten = send the form
• skicka in blanketten = send in / submit the form

If you are talking about handing in paperwork, applications, tax forms, and similar things, skicka in is often the right choice.

As a statement, the subject comes first:

• Du kan skicka in blanketten så snabbt som möjligt.

As a yes/no question, the verb moves in front:

• Kan du skicka in blanketten så snabbt som möjligt?

That verb-first pattern is one of the basic features of Swedish questions.

Modern Swedish uses du with almost everyone, even in many professional situations.

So Kan du ... ? is normal whether you are speaking to:

• a colleague
• a customer
• a teacher
• an official

Swedish does not use formal you in the way some other European languages do. If you want to sound more polite, you usually change the phrasing, not the pronoun:

• Kan du ... ?
• Skulle du kunna ... ?
• Kan du vara snäll och ... ?

The main stress usually falls on the important content words:

Kan du SKICKA in BLANKETTEN så SNABBT som MÖJLIGT?

A few helpful notes:

• kan du is often said fairly lightly
• skicka in gets clear stress because it expresses the action
• blanketten and möjligt also stand out

In natural speech, the sentence flows quite smoothly rather than sounding word-by-word.