Jeg læser mærket på skjorten, før jeg vasker den.

Because mærket is the definite form: the label.

In Danish, the definite article is usually added to the end of the noun instead of being a separate word like English the.

• et mærke = a label / a mark
• mærket = the label

Here, the sentence refers to a specific label, namely the one on the shirt, so Danish uses mærket.

For the same reason: skjorten means the shirt.

• en skjorte = a shirt
• skjorten = the shirt

Danish often uses the definite form when English would also say the. Since this is a particular shirt, the definite form is natural.

That is one of the basic features of Danish grammar. In many cases, definiteness is expressed with a suffix attached to the noun.

Examples:

• en bog = a book
• bogen = the book
• et hus = a house
• huset = the house

In your sentence:

• mærket = the label
• skjorten = the shirt

This is completely normal in Danish and is something English speakers need to get used to.

På skjorten means on the shirt.

The preposition på usually means on, and here it tells you where the label is located. So mærket på skjorten is the label on the shirt.

That is very close to English structure:

• mærket = the label
• på skjorten = on the shirt

So the phrase is built very literally.

Den means it, and here it refers to skjorten.

So:

• jeg vasker den = I wash it

Since skjorte is a common gender noun in Danish, the pronoun used for it is den.

Compare:

• en skjorte → den
• et hus → det

So den replaces skjorten to avoid repeating the noun.

Because før introduces a subordinate clause, and Danish word order changes in subordinate clauses.

In a normal main clause, Danish is a verb-second language:

• Jeg læser mærket.

But after a subordinating word like før, the clause usually has subject + verb order:

• før jeg vasker den

So this is the expected word order.

A useful contrast:

• Jeg vasker den ikke. = main clause
• før jeg vasker den = subordinate clause

No inversion happens after før inside that clause.

Because Danish normally uses a comma before a subordinate clause.

Here, før jeg vasker den is a subordinate clause introduced by før, so the comma is standard Danish punctuation.

English is often less strict about this kind of comma, but in Danish it is very common and expected in writing.

Yes, in many contexts you could.

Mærke can mean several things depending on context, such as:

• mark
• sign
• brand
• label

In clothing contexts, mærket can naturally be understood as the label/tag, especially if the meaning has already been made clear.

But etiketten is also possible if you want to be very explicit about the label/tag.

The exact choice can depend on context and style.

Yes. At læse means to read, and it works the same way here as in English.

• Jeg læser mærket = I read the label

This is perfectly natural if you mean reading washing instructions, size information, fabric details, and so on.

Both are in the present tense.

• jeg læser = I read / I am reading
• jeg vasker = I wash / I am washing

Like English, Danish present tense can often cover both a general present and an action happening around now, depending on context.

So the sentence can mean something like:

• I read the label before I wash it
• I am reading the label before washing it

The exact interpretation depends on the situation.

Unfortunately, this is something you mostly have to learn with each noun.

• et mærke
• en skjorte

Then the definite forms follow from that:

• et mærke → mærket
• en skjorte → skjorten

And the pronouns match too:

• en-words usually take den
• et-words usually take det

So because skjorte is an en-word, the sentence later uses den.

Yes. For example:

Før jeg vasker den, læser jeg mærket på skjorten.

This means the same thing.

Notice what happens in the main clause after the fronted subordinate clause:

• læser jeg instead of jeg læser

That is because Danish keeps the finite verb in second position in main clauses. So when Før jeg vasker den comes first, the verb læser has to come before the subject jeg in the main clause.

That is a very common Danish pattern.

They are related, but not always equally natural.

• mærket på skjorten = the label on the shirt
• skjortens mærke = the shirt’s label / the label of the shirt

The på phrase is usually the more straightforward and natural way to say it in everyday Danish here. The possessive form skjortens is possible, but it can sound a bit more formal or less idiomatic in this context.

So mærket på skjorten is a very natural choice.