Arrangören hälsar alla välkomna.

Because arrangören is the definite singular form of arrangör (organizer).

In Swedish, the equivalent of the is often added to the end of the noun instead of being a separate word:

• en arrangör = an organizer
• arrangören = the organizer

So -en here is the definite ending.

Swedish usually puts definiteness on the noun itself with a suffix.

So instead of saying the organizer, Swedish normally says:

• arrangören

This is very common in Swedish. English uses a separate article; Swedish often uses an ending.

Hälsar is the present tense of hälsa.

• hälsa = to greet / to welcome / to say hello
• hälsar = greets / welcomes

So the sentence is in the present tense: The organizer welcomes everyone.

No. Hälsa has a broader meaning than just welcome.

It can mean things like:

• to greet
• to say hello
• to welcome

In this sentence, because of välkomna, it specifically means to welcome. The pattern is:

• hälsa någon välkommen / välkomna = welcome someone

So hälsar alla välkomna means literally something like greets everyone welcome, but in natural English that is simply welcomes everyone.

Because alla is the Swedish form used for everyone / everybody / all people.

Compare:

• all = all, whole, entire (often used before singular mass nouns)
• alla = all, everyone, all people, all things

In this sentence, alla means everyone.

Because välkomna agrees with alla, which is plural in meaning.

Here, välkommen / välkomna is not the main verb. It is an adjective describing the people being welcomed.

Compare:

• Han hälsar gästen välkommen. = He welcomes the guest.
• Han hälsar gästerna välkomna. = He welcomes the guests.

So:

• välkommen = singular
• välkomna = plural

Since alla means everyone / all people, Swedish uses the plural form välkomna.

No. Välkomna here is an adjective, not a verb.

The only finite verb in the sentence is hälsar.

You can think of the structure like this:

• Arrangören = subject
• hälsar = verb
• alla = object
• välkomna = adjective describing the object

So the organizer is welcoming everyone, and everyone is being described as welcome.

The word order is:

Subject + Verb + Object + Object complement

So:

• Arrangören = subject
• hälsar = verb
• alla = object
• välkomna = complement describing the object

This is a very normal Swedish main-clause pattern. Swedish also follows the verb-second rule in main clauses, and here the verb is in second position:

1. Arrangören
2. hälsar

Yes, it is a very natural and common pattern, especially in formal or semi-formal situations.

The expression:

• hälsa någon välkommen / välkomna

is a standard way to say welcome someone.

You might hear it from:

• event organizers
• hosts
• speakers
• companies
• schools

So Arrangören hälsar alla välkomna sounds like something you could see on a sign, website, program, or announcement.

Then välkommen would usually be singular instead of plural.

For example:

• Arrangören hälsar gästen välkommen. = The organizer welcomes the guest.

But with more than one person, or with alla, you use välkomna:

• Arrangören hälsar gästerna välkomna.
• Arrangören hälsar alla välkomna.

So the form of välkommen / välkomna depends on who is being welcomed.

The ö sound does not exist in standard English, so it often feels tricky.

A rough guide:

• arrangören ≈ ah-rang-YUR-en

The ö is a rounded vowel. To practice it, try saying an e-like sound while rounding your lips.

Also note that the stress is typically on -gör- in this word:

• ar-rang-gör-en

You do not need perfect pronunciation right away, but paying attention to ö is useful because it distinguishes words in Swedish.