Vi fejrer jul den fireogtyvende december.

Vi means we, and fejrer means celebrate.

So:

• Vi = we
• fejrer = celebrate

Fejrer is the present tense of fejre. Danish uses the present tense here much like English does for general facts or regular customs.

Because Danish finite verbs change form for tense, not for person.

The basic verb is fejre = to celebrate.
In the present tense, it becomes fejrer:

• at fejre = to celebrate
• fejrer = celebrate / celebrates / are celebrating depending on context

Unlike English, Danish does not change the verb for I / you / we / they. So the same present-tense form is used with all subjects:

• jeg fejrer
• du fejrer
• vi fejrer

Because in Danish, fejre jul is the normal expression for celebrate Christmas.

Here, jul is used without the definite ending. This is similar to how English says celebrate Christmas, not celebrate the Christmas.

Compare:

• Vi fejrer jul = We celebrate Christmas
• Julen = the Christmas period / Christmas in a more definite or specific sense

So in this sentence, the bare noun jul is the natural choice.

Because Danish capitalization rules are different from English.

In Danish:

• common nouns are not capitalized
• months are not capitalized
• holidays are usually not capitalized either

So:

• jul, not Jul
• december, not December

English capitalizes these words, but Danish normally does not.

Den is part of the standard way Danish expresses calendar dates.

The pattern is:

den + ordinal number + month

So:

• den fireogtyvende december = the twenty-fourth of December

Here, den works a bit like the in English date expressions.

You will see the same pattern in other dates too:

• den første maj = the first of May
• den syttende juni = the seventeenth of June

Because dates use an ordinal number, not a cardinal number.

• fireogtyve = twenty-four
• fireogtyvende = twenty-fourth

In English, you also usually use the ordinal in dates:

• the twenty-fourth of December

So Danish does the same:

• den fireogtyvende december

In everyday writing, people very often write this as:

• den 24. december

But when read aloud, it is still read as an ordinal.

Because Danish often uses dates without a preposition in this kind of sentence.

English says:

• on the 24th of December

But Danish commonly says simply:

• den fireogtyvende december

So:

• Vi fejrer jul den fireogtyvende december.

This is completely normal Danish.
A similar thing happens with days:

• Vi ses mandag. = See you on Monday.

English needs on here, but Danish often does not.

No. It is correct, but not the only common form.

You will also very often see:

• den 24. december

That is the normal numeric way to write the same date.

So these are equivalent in meaning:

• den fireogtyvende december
• den 24. december

The fully written-out version may feel a bit more formal or careful, while the numeric version is very common in everyday writing.

Because that is the normal Danish date order.

Danish uses:

day + month

So:

• den fireogtyvende december
• den 24. december

This is similar to British English date order, not the common American month-day order.

This is a normal main clause with the subject first:

• Vi = subject
• fejrer = finite verb
• jul = object
• den fireogtyvende december = time expression

So the basic order is:

subject + verb + object + time

That gives:

Vi fejrer jul den fireogtyvende december.

But Danish is a V2 language, which means the finite verb usually stays in the second position in main clauses. So you can also move the time expression to the front:

• Den fireogtyvende december fejrer vi jul.

That is also correct.

Because Danish numbers are built differently from English numbers.

Fireogtyve literally means something like four-and-twenty:

• fire = four
• og = and
• tyve = twenty

So fireogtyve = twenty-four

Then Danish adds an ordinal ending to make fireogtyvende = twenty-fourth.

This is one reason Danish numbers often feel difficult to English speakers: the smaller number often comes before the larger one in the word.

In standard Danish writing, the dot is normally used with the numeral in dates:

• den 24. december

That dot shows the number is being used as an ordinal date value.

So den 24. december is the standard written form.
Writing den 24 december may be understood, but it is not the usual standard spelling.

Yes, it reflects a specifically Danish way of talking about Christmas.

In Denmark, the main Christmas celebration is traditionally on the evening of 24 December, so the sentence sounds very natural culturally:

• Vi fejrer jul den fireogtyvende december.

An English speaker may expect Christmas Day, 25 December, to be the main celebration, but in Denmark the 24th is typically the key day for family celebration, dinner, and presents.