Vi holder nytår hos mine forældre den enogtredivte december.

In Danish, holde is very often used for celebrating or marking an occasion.

So holde nytår means something like celebrate New Year / spend New Year.

This is part of a wider pattern:

• holde jul = celebrate Christmas
• holde fødselsdag = celebrate a birthday
• holde fest = have a party

So even though holde literally often means hold, in sentences like this it is an idiomatic Danish choice.

In everyday Danish, nytår often refers to the New Year celebration, especially the evening/night around the turn of the year.

A useful distinction is:

• nytår = New Year, often the celebration in general
• nytårsaften = New Year’s Eve
• nytårsdag = New Year’s Day

So in this sentence, holder nytår is naturally understood as celebrating New Year’s Eve / the New Year celebration, not New Year’s Day.

Hos is used when you mean at someone’s place, with someone, or at the home/business of a person.

So:

• hos mine forældre = at my parents’ house / with my parents

This is different from a more general location word like i or på.

Compare:

• Jeg er hos min ven. = I’m at my friend’s place.
• Jeg er i huset. = I’m in the house.
• Jeg er på skolen. = I’m at the school.

So hos is the natural choice because the location is defined by the people, not just by a building.

Because forældre is plural, you need the plural possessive mine.

The possessive forms are:

• min for a common-gender singular noun
• mit for a neuter singular noun
• mine for plural nouns

So:

• min ven = my friend
• mit hus = my house
• mine forældre = my parents

Also, forældre means parents, so it is plural by meaning as well.

The singular is forælder, meaning parent.

So:

• en forælder = a parent
• forældre = parents

In the sentence, mine forældre is plural, so everything agrees with that plural form.

Danish usually does not use a preposition where English says on before a specific date.

So English says:

• on the 31st of December

But Danish normally says simply:

• den enogtredivte december

No extra word is needed before the date.

That is very normal in Danish time expressions.

When Danish gives a date with an ordinal number, it normally uses:

• den
  • ordinal number + month

So:

• den første januar = the first of January
• den femte maj = the fifth of May
• den enogtredivte december = the thirty-first of December

Here den works together with the ordinal form enogtredivte.

You will also often see dates written with numerals:

• den 31. december

That is probably more common in everyday writing than spelling out the whole number in words.

It is the ordinal form of enogtredive = thirty-one.

Danish numbers are built a bit differently from English:

• en = one
• og = and
• tredive = thirty

So:

• enogtredive = one-and-thirty = 31

To make it ordinal, Danish uses an ending such as -te:

• enogtredive = thirty-one
• enogtredivte = thirty-first

This is one of those forms that learners usually just have to get used to, because Danish number words are not always very transparent at first.

Because in Danish, months are not capitalized unless they begin a sentence.

So Danish writes:

• januar
• februar
• december

The same is true for many holidays and languages as well. This is different from English, where December must be capitalized.

You can move it.

The original sentence is completely fine:

• Vi holder nytår hos mine forældre den enogtredivte december.

But Danish often allows the time expression to come earlier, especially for emphasis:

• Den enogtredivte december holder vi nytår hos mine forældre.

That version puts more focus on the date.

A key Danish rule is that the finite verb usually stays in the second position in main clauses, so when you move the date to the front, holder still comes second.

Yes, often you could, depending on exactly what you want to stress.

• Vi holder nytår hos mine forældre. = We celebrate/spend New Year at my parents’ place.
• Vi holder nytårsaften hos mine forældre. = We spend New Year’s Eve at my parents’ place.

Nytårsaften is more specific. Nytår is a little broader and can sound more like the whole celebration around the New Year.

In many everyday situations, both would be understood, but nytårsaften is the clearest if you want to emphasize the evening itself.