Lukten är underbar.

Because -en is the definite ending. Swedish usually puts the at the end of the noun instead of using a separate word.

• lukt = smell / a smell
• lukten = the smell

So Lukten är underbar means The smell is wonderful.

The dictionary form is lukt.

When you look up Swedish nouns, you usually find the indefinite singular form:

• en lukt = a smell

From that, you can build:

• lukten = the smell

So lukten is the definite singular form of lukt.

Because lukt is an en-word (also called common gender).

For many en-words, the definite singular ends in -en:

• en bok → boken
• en stol → stolen
• en lukt → lukten

If it were an ett-word, the definite ending would usually be -et instead.

Because the adjective agrees with the noun.

Here, lukt is an en-word, so the predicate adjective stays in the common-gender singular form:

• Lukten är underbar.
• Boken är intressant.

You use underbart with an ett-word:

• Vädret är underbart. = The weather is wonderful.

So underbar matches lukten.

Yes. Underbar is an adjective meaning wonderful.

In this sentence it comes after är and describes the subject lukten, so it is a predicate adjective:

• Lukten = subject
• är = verb
• underbar = adjective describing the subject

This works like English The smell is wonderful.

Är means is / are / am depending on context, and it comes from the verb vara = to be.

Here it means is:

• Lukten är underbar. = The smell is wonderful.

Useful forms of vara:

• är = present
• var = past
• vara = infinitive

Because Swedish often expresses definiteness by attaching it to the noun itself.

So instead of:

• the smell

Swedish says:

• lukt-en

This is one of the first big differences English speakers notice. Swedish can use separate words like den/det/de, but in a simple sentence like this, the definite ending on the noun is enough.

Yes. It has the standard word order for a basic statement:

• Lukten = subject
• är = verb
• underbar = complement

So it follows the common pattern:

Subject + verb + complement

Very straightforward Swedish sentence structure.

Yes, and in many situations that may sound more natural.

Both words can relate to smell, but there is often a nuance:

• lukt = smell, often neutral or sometimes negative
• doft = fragrance / scent, often positive

So if you are talking about a pleasant smell, many speakers might prefer:

• Doften är underbar.

But Lukten är underbar is still understandable and grammatically correct.

Not always, but it often leans more neutral or negative than doft.

For example:

• Det luktar konstigt. = It smells strange.
• En obehaglig lukt = an unpleasant smell

If you want to emphasize that the smell is pleasant, doft is often the more natural choice. Still, context matters, and lukt can be used in a neutral way too.

A simple approximate pronunciation for an English speaker is:

LUK-ten air UN-der-bar

A few notes:

• lukten has stress on the first syllable: LUK-
• är sounds a bit like air
• underbar has stress on the last part: -bar

The exact Swedish vowels are not exactly like English, but that approximation is good enough to get started.

Yes, but not with lukten.

You would use underbart after är when the subject is an ett-word:

• Huset är underbart. = The house is wonderful.

You can also see underbart used more like an adverb in expressions such as:

• Det är underbart. = It is wonderful.

But with lukten, the correct form is underbar.

The common forms are:

• en lukt = a smell
• lukten = the smell
• lukter = smells
• lukterna = the smells

So if you wanted a plural sentence, you could say:

• Lukterna är underbara. = The smells are wonderful.

Notice that the adjective changes to underbara in the plural.