Poplatková povinnost je v obecně závazné vyhlášce.

It is the subject of the sentence, so it is in the nominative singular.

• povinnost = a feminine singular noun
• poplatková = an adjective agreeing with it in gender, number, and case

So:

• poplatková povinnost = nominative singular feminine

That is why the adjective ends in -á.

Poplatková is an adjective formed from poplatek (fee, charge).

It means something like:

• fee-related
• concerning a fee
• connected with a fee

So poplatková povinnost is literally something like fee-related obligation, although in natural English it is usually expressed more smoothly.

Yes, povinnost is feminine.

A lot of Czech nouns ending in -ost are feminine, for example:

• možnost
• společnost
• povinnost

Because povinnost is feminine, the adjective agreeing with it must also be feminine:

• poplatková povinnost

Je is the 3rd person singular present form of být (to be).

It is used because the subject is singular:

• Poplatková povinnost = one obligation
• therefore je = is

So grammatically the structure is simply:

• subject + je + prepositional phrase

In normal full sentences, Czech usually keeps je here.

Because the preposition v meaning in normally takes the locative when it expresses location.

The dictionary form is:

• obecně závazná vyhláška

But after v, it changes to the locative singular:

• v obecně závazné vyhlášce

Here is the change:

• vyhláška → vyhlášce
• závazná → závazné

So the whole phrase has to match the locative.

Because obecně modifies the adjective závazná / závazné, not the noun directly.

It means generally, so:

• obecně závazná = generally binding

This is a common Czech legal expression. The structure is:

• obecně = adverb
• závazná = adjective
• vyhláška = noun

So obecně does not change for case, gender, or number.

It is locative singular.

Why?

• the preposition v = in
• with location, v requires the locative

So:

• vyhláška = nominative singular
• v ... vyhlášce = locative singular

This is a very common pattern in Czech:

• v zákoně
• v dokumentu
• v knize
• v obecně závazné vyhlášce

It is a fixed legal expression in Czech law. It refers to a type of officially binding regulation, often translated as something like:

• generally binding ordinance
• generally binding decree
• binding bylaw

For a learner, the important point is that this whole phrase often behaves almost like one set expression.

Because Czech has no articles.

English says:

• the obligation
• the ordinance

Czech usually expresses definiteness from context, not with a separate word. So:

• Poplatková povinnost je v obecně závazné vyhlášce.

can still mean a definite, specific obligation and a specific ordinance, even though there is no separate word for the.

Yes. Czech word order is fairly flexible.

The original sentence is:

• Poplatková povinnost je v obecně závazné vyhlášce.

You could also say:

• V obecně závazné vyhlášce je poplatková povinnost.

Both are grammatical, but the emphasis changes.

• Starting with Poplatková povinnost makes that the topic.
• Starting with V obecně závazné vyhlášce puts more focus on where it is stated.

In legal or formal writing, word order is often chosen for information structure rather than strict syntax.

Yes. With documents, texts, and regulations, Czech often uses v to mean in in the sense of contained in or stated in.

So v obecně závazné vyhlášce means that the obligation is found, stated, or laid down in that legal document.

This is very natural in formal Czech.

No, it is quite formal and legal/administrative in style.

A native speaker would understand it, but it sounds like official language rather than casual conversation.

That is mainly because of expressions like:

• poplatková povinnost
• obecně závazná vyhláška

These are typical of bureaucratic or legal Czech.