Katten sover i transportburen.

Because katten is the definite form of katt.

• en katt = a cat
• katten = the cat

In Swedish, definiteness is often shown by adding an ending to the noun instead of using a separate word like the in English.

So:

• Katt sover... would not work here
• Katten sover... = The cat is sleeping...

Swedish usually puts the definite meaning at the end of the noun.

Compare:

• en katt = a cat
• katten = the cat

So English uses a separate word:

• the cat

But Swedish often uses a suffix:

• katt
  • -en → katten

That is why you do not need a separate word for the here.

Sover is the present tense of the verb sova = to sleep.

Examples:

• jag sover = I sleep / I am sleeping
• katten sover = the cat sleeps / the cat is sleeping

Swedish present tense is often made by adding -r to the verb stem:

• sova → sover

Also, Swedish does not change the verb depending on the subject:

• jag sover
• du sover
• katten sover
• vi sover

It stays sover for all of them.

It can mean both, depending on context.

Swedish present tense often covers both:

• The cat sleeps
• The cat is sleeping

So Katten sover i transportburen could be understood as either a general present statement or something happening right now. Usually the situation makes it clear.

This is the normal basic Swedish word order for a simple statement:

subject + verb + other information

So here:

• Katten = subject
• sover = verb
• i transportburen = prepositional phrase telling where

This is very similar to normal English word order:

• The cat
  • is sleeping
    • in the carrier

I means in here.

It is a very common Swedish preposition:

• i huset = in the house
• i bilen = in the car
• i transportburen = in the carrier / crate

Be careful: Swedish i is a preposition, while English speakers may first notice that it looks like the English pronoun I. In Swedish, it does not mean I.

It is a compound noun in the definite form.

It is built from:

• transport = transport
• bur = cage, crate, carrier

Together:

• transportbur = transport cage / pet carrier
• transportburen = the transport cage / the pet carrier

Swedish makes compound nouns very freely, much more than English often does. So instead of using several separate words, Swedish often joins them into one long noun.

Because bur is an en-word, and its definite singular form is made with -en.

So:

• en bur = a cage / crate
• buren = the cage / crate

When it appears inside the compound noun, the whole word becomes:

• en transportbur
• transportburen

The definite ending is added to the whole compound, not to the first part.

Unfortunately, this usually has to be learned with the noun.

In Swedish, nouns are mainly divided into two genders:

• en-words
• ett-words

Bur is an en-word, so:

• en bur
• buren

That also affects adjectives and other forms in longer phrases. A good habit is to learn Swedish nouns together with their article:

• en katt
• en bur
• en transportbur

Yes, but it means something different.

• i transportburen = in the carrier / in the transport cage
• i en transportbur = in a carrier / in a transport cage

So the difference is definite versus indefinite:

• transportburen = a specific carrier already known in the context
• en transportbur = any one carrier, not specifically identified

Because transportburen by itself already means the carrier.

In Swedish, you normally do not add den before a definite noun unless there is usually an adjective or some special structure.

Compare:

• transportburen = the carrier
• den stora transportburen = the big carrier

So:

• without adjective: transportburen
• with adjective: den stora transportburen

It would be:

En katt sover i en transportbur.

That means A cat is sleeping in a carrier.

Compare the two:

• Katten sover i transportburen. = The cat is sleeping in the carrier.
• En katt sover i en transportbur. = A cat is sleeping in a carrier.

This is a useful comparison because it shows both definite forms clearly:

• en katt → katten
• en transportbur → transportburen

Yes. Swedish uses compound nouns very naturally.

A few similar examples are:

• hundbur = dog cage / dog crate
• kattbur = cat cage / cat carrier
• sjukhusrum = hospital room
• sommarhus = summer house

For English speakers, one important habit is to look for the smaller parts inside a long Swedish noun. That often makes the word much easier to understand and remember.

A rough guide for an English speaker would be something like:

KAH-ten SO-ver ee trans-PORT-boo-ren

A few notes:

• katten has two syllables: katt-en
• sover is also two syllables: so-ver
• i is pronounced like a long ee
• u in buren does not sound exactly like English oo, but boo-ren is a helpful rough approximation

The exact Swedish vowels are a bit different from English ones, but this approximation is enough to get started.