W tym roku spędzę Sylwestra w domu z rodziną.

Literally, w tym roku is in this year, but in natural English we usually just say this year.

Polish often uses w + locative in time expressions like this. That is why:

• ten → tym
• rok → roku

So w tym roku is the normal Polish way to say this year.

Spędzę means I will spend.

It is:

• 1st person singular: I
• from the verb spędzić
• in a perfective form

A very important Polish point: with perfective verbs, forms that look like present-tense forms often actually refer to the future. So spędzę means I will spend, not I spend.

Because spędzić is a perfective verb.

In Polish:

• imperfective verbs usually make the future with będę + infinitive / past-like form
• perfective verbs use their own simple future form

So:

• spędzę = I will spend is correct here
• będę spędzać would use the imperfective verb spędzać, and it would sound different in nuance

For a single completed event like New Year’s Eve, spędzę is the most natural choice.

Because it is the direct object of spędzę.

The basic form is Sylwester, but after a verb like spędzić (to spend), it goes into the accusative case:

• Sylwester → Sylwestra

This noun declines like a masculine animate noun, so the accusative singular ends in -a.

Yes. Sylwester is both:

• a male first name
• the usual Polish word for New Year’s Eve / the New Year’s Eve celebration

So in this sentence, Sylwestra means New Year’s Eve, not a person.

You will often see it capitalized in this holiday/celebration sense.

Because w here means in/at, and it expresses location, not movement.

So:

• w domu = at home / in the house
• do domu = to the house / home (movement toward it)

After w meaning location, dom changes to the locative form:

• dom → domu

Because z meaning with requires the instrumental case.

So:

• rodzina → rodziną

That gives:

• z rodziną = with family / with the family

A useful warning: z can also mean from/out of, and then it takes a different case:

• z domu = from the house

So z does not always work the same way.

Because Polish often leaves out subject pronouns when the verb already shows who the subject is.

The ending -ę in spędzę already tells you it means I will spend. So ja is not necessary.

You can add ja only for emphasis or contrast:

• Ja spędzę Sylwestra w domu... = I will spend New Year’s Eve at home...

Yes, absolutely.

• z rodziną = with family / with the family
• z moją rodziną = with my family

In Polish, possessive words like my are often omitted when the meaning is already obvious from context. So the shorter z rodziną sounds very natural.

No. Polish word order is fairly flexible.

The original sentence:

• W tym roku spędzę Sylwestra w domu z rodziną.

is natural and neutral.

But you can move things around for emphasis, for example:

• Sylwestra spędzę w tym roku w domu z rodziną.
  Emphasis on New Year’s Eve
• W domu spędzę Sylwestra w tym roku z rodziną.
  Emphasis on at home

So the original order is not the only possible one, but it is a very normal one.

Because Polish has no articles.

English needs words like a and the, but Polish does not use them. Whether something is definite or indefinite is usually understood from:

• context
• word order
• the situation

So Polish simply says:

• w domu
• z rodziną

without any separate word for the or a.