Learn Hardcore Czech: V zimě je park prázdný a často tam není nikdo. - In winter the park is empty and often there is nobody there.

Zimě is locative singular of the feminine noun zima.
For many feminine nouns ending in -a, the locative singular ends in -ě or -e.
The pattern here is:

Nominative: zima (winter)
Locative: (o) zimě, v zimě (about/in winter)

You’ll see the same pattern with similar words:

škola → ve škole (school → in school)
kavárna → v kavárně (café → in the café)

Can I also say Park je v zimě prázdný? Is it different?

Yes, Park je v zimě prázdný is correct.
Both V zimě je park prázdný and Park je v zimě prázdný mean the same thing.

The difference is only in emphasis / focus:

V zimě je park prázdný highlights the time first: “In winter, the park is empty.”
Park je v zimě prázdný starts with the park: “The park is empty in winter.”

In everyday speech both are natural.

What exactly is the function of je here?

Je is the 3rd person singular of být (to be), so it’s just “is”.
In the first clause it’s a linking verb (copula) connecting the subject and the adjective:

park (subject) + je (is) + prázdný (empty).

So the basic structure is the same as in English: “The park is empty.” → Park je prázdný.

Why is it prázdný and not prázdno?

Prázdný is an adjective meaning empty, and it must agree with the noun park (masculine inanimate, singular).

park (masc. sg.) → prázdný (masc. sg. adjective)

Prázdno is a neuter noun meaning emptiness or can function like an adverbial “it’s empty” in some patterns:

Je tady prázdno. – It’s empty here. (literally: “there is emptiness here”)

Here we’re directly describing the park as an object, so we use the adjective: park je prázdný.

What does tam add here, and how is it different from tady?

Tam means there, referring to a place away from the speaker.
Tady means here, near the speaker.

In často tam není nikdo, tam refers back to park:

literally: “often there is nobody there (in that place)”

If you were standing in the park yourself, you could also say Tady často není nikdo. – “There’s often nobody here.”

Is the word order často tam není nikdo fixed? Can I say Tam často není nikdo or Často není tam nikdo?

The most natural versions here are:

V zimě je park prázdný a často tam není nikdo.
V zimě je park prázdný a tam často není nikdo.

Both are fine; they just shift the rhythm and slight emphasis.

Často není tam nikdo is grammatically possible, but it sounds less natural; Czech normally avoids putting tam after the verb in this way if there’s also a negative pronoun (nikdo) later. Native speakers tend to keep short adverbs like tam closer to the beginning of the clause.

Why is it tam není nikdo and not tam nikdo není?

You can actually say tam nikdo není too; it’s also correct.
Both mean “there is nobody there”, but the focus is slightly different:

tam není nikdo tends to emphasize the non-existence of people there (“there’s nobody at all”).
tam nikdo není gives a bit more weight to nikdo (“no one is there”).

In neutral context, they’re practically interchangeable, and both sound natural.

Does není nikdo count as a “double negative”? Why isn’t it wrong in Czech?

Yes, není nikdo is a double negative from an English point of view:

není = is not
nikdo = nobody (a negative pronoun)

In Czech, double negation is standard and required in this kind of sentence.
To say “nobody is there” you must use both the negative verb and the negative pronoun:

Není tam nikdo. – There is nobody there.

Using a positive pronoun here (někdo) would change the meaning:

Není tam někdo. usually suggests: “Isn’t someone there?” / “I think someone might be there, isn’t there?” (context-dependent, but not “there’s nobody”).

What is the difference between nikdo and někdo?

někdo = someone / somebody (neutral or positive)
nikdo = no one / nobody (negative pronoun)

With negation you normally use nikdo:

Není tam nikdo. – There is nobody there.

With a positive verb you use někdo:

Je tam někdo. – There is someone there.

Why isn’t there a word for “the” in park? Shouldn’t it be “the park”?

Czech has no articles (no “a/an/the”).
Whether it’s “a park” or “the park” is understood from context, not from a separate word.

In this sentence, context makes park specific – the listener can imagine which park you mean – so the natural English translation uses “the park”, but the Czech form is just park.

Could I translate je park prázdný as “there is an empty park”?

Not in this word order.
Je park prázdný means “the park is empty” (subject + verb + adjective).

To say “there is an empty park”, Czech would typically use a different structure and context, for example:

Je tam prázdný park. – There is an empty park there.

So in the original sentence, park is clearly the subject, not just being introduced as “there is a park”.

Is the subject pronoun like on (he/it) ever needed here, like On je prázdný?

In this sentence, no. The subject is already the noun park, so adding on would be redundant.

Czech usually drops subject pronouns when the subject is clear from the noun or from the verb ending:

Park je prázdný. – The park is empty.
On je prázdný. – He/it is empty. (used only if on is the subject in the context, not when park has just been named explicitly)

So the natural form is just Park je prázdný, without on.