Az idei megállapodás érvényes.

Literally, it is:

• Az = the
• idei = this year’s
• megállapodás = agreement
• érvényes = valid / in force / effective

So the sentence means The agreement for this year is valid or This year’s agreement is valid.

Idei is an adjective meaning of this year or this year’s.

Compare:

• idén = this year → an adverb of time
  
  • Idén sokat dolgozom. = I am working a lot this year.
• idei = this year’s → an adjective modifying a noun
  
  • az idei megállapodás = this year’s agreement

So in your sentence, idei describes megállapodás.

Here az is the definite article the.

Hungarian uses two forms of the definite article:

• a
• az

Which one is used depends on the sound that follows. Before a vowel sound, Hungarian uses az.

Since idei starts with a vowel, you say:

• az idei megállapodás

not

• a idei megállapodás

Although az can also mean that in other contexts, here it is just the article the.

In Hungarian, in the present tense, third person, the verb to be is usually omitted.

So:

• A megállapodás érvényes.
  literally: The agreement valid.
  natural English: The agreement is valid.

This is completely normal in Hungarian.

But in other persons, the verb appears:

• Én fáradt vagyok. = I am tired.
• Te fáradt vagy. = You are tired.

So the missing is in your sentence is standard Hungarian grammar.

Érvényes is an adjective. It means:

• valid
• effective
• in force

In this sentence, it is the predicate adjective:

• Az idei megállapodás érvényes.
• This year’s agreement is valid.

You will also see it in phrases like:

• érvényes jegy = a valid ticket
• érvényes útlevél = a valid passport

The ending -ás / -és often forms a noun from a verb, similar to English -ing, -tion, or a verbal noun.

Here:

• megállapodik = to come to an agreement / to reach an agreement
• megállapodás = agreement / settlement

So megállapodás is a noun meaning the result or act of agreeing.

This pattern is very common in Hungarian.

Because they do two different jobs.

1. idei is an attributive adjective: it directly modifies the noun.

   • az idei megállapodás = this year’s agreement

2. érvényes is the predicate of the sentence: it tells you something about the noun.

   • Az idei megállapodás érvényes. = This year’s agreement is valid.

This is similar to English:

• the valid agreement = adjective before noun
• the agreement is valid = adjective after is

Hungarian works similarly, except that the present-tense is is omitted here.

Yes, but changing the word order changes the emphasis.

Neutral order:

• Az idei megállapodás érvényes.
• This year’s agreement is valid.

If you move érvényes to the front:

• Érvényes az idei megállapodás.

This gives more emphasis to érvényes, something like:

• The agreement for this year is indeed valid
• It is valid, the agreement for this year

So the original sentence is the most neutral and straightforward version.

You can use similar forms with other time expressions too. Hungarian often creates adjectives meaning of this X.

Examples:

• mai = today’s
• tegnapi = yesterday’s
• holnapi = tomorrow’s
• idei = this year’s
• tavalyi = last year’s

So idei belongs to a very common and useful pattern.

A rough pronunciation guide is:

• Az ≈ awz
• idei ≈ ee-deh-ee
• megállapodás ≈ meh-gaa-lah-po-daash
• érvényes ≈ air-vay-nyesh

A few useful points:

• á is a long a
• é is a long e
• ny sounds like the ny in Spanish señor
• stress in Hungarian is always on the first syllable of each word:
  • AZ
  • I-de-i
  • MEG-ál-la-po-dás
  • ÉR-vé-nyes

It can be broader. Depending on context, érvényes can mean:

• valid
• effective
• in force
• applicable

So in this sentence, it could mean the agreement is:

• legally valid,
• still in effect,
• officially recognized,
• not expired or cancelled.

The exact nuance depends on the situation.

Because Hungarian does not have to express that idea with possession in the same way English does.

English uses a possessive form:

• this year’s agreement

Hungarian often uses an adjective instead:

• idei megállapodás

So rather than literally saying the agreement of this year with a possessive structure, Hungarian uses idei, which already means this year’s.

That is the natural way to say it.