A hibajegyzék hosszú.

A is the Hungarian definite article, so it corresponds to the in English.

A useful extra point:

• a is used before a consonant sound
• az is used before a vowel sound

So:

• a hibajegyzék = the bug list / the error list
• az asztal = the table

In Hungarian, the verb van (to be) is usually left out in the present tense, third person when the predicate is a noun or an adjective.

So Hungarian says literally:

• A hibajegyzék hosszú.
• The bug list long.

But in natural English, that means:

• The bug list is long.

Compare:

• Én hosszú vagyok would be wrong for this meaning, but in first person you do need the verb:
• Én fáradt vagyok = I am tired
• Te fáradt vagy = You are tired
• Ő fáradt = He/She is tired

So in your sentence, leaving out is is completely normal.

Yes, hibajegyzék is one word because Hungarian very often forms compound nouns by writing the parts together.

It is built from:

• hiba = error, fault, bug
• jegyzék = list, register, catalog

So hibajegyzék is literally something like:

• error-list
• bug-list

This is very common in Hungarian. English sometimes uses two words where Hungarian prefers one compound word.

In Hungarian, adjectives come before a noun only when they directly describe it inside a noun phrase.

So:

• a hosszú hibajegyzék = the long bug list

But in your sentence, hosszú is not just modifying the noun inside the phrase. It is the predicate of the sentence:

• A hibajegyzék hosszú. = The bug list is long.

So the structure is:

• A hibajegyzék = subject
• hosszú = predicate adjective

That is why the adjective comes after the noun here.

Not in the way an English speaker might expect from languages like French or German.

Hungarian adjectives do not agree for:

• gender
• grammatical case in this kind of sentence

And Hungarian has no grammatical gender anyway.

In this sentence, hibajegyzék is singular, so:

• A hibajegyzék hosszú.

If the subject is plural, the predicate adjective is usually plural too:

• A hibajegyzékek hosszúak. = The bug lists are long.

So the singular form is hosszú, and the plural predicate form is hosszúak.

Yes, that is possible.

Hungarian word order is flexible, and changing the order often changes the focus or emphasis, not the basic meaning.

• A hibajegyzék hosszú.
  Neutral statement: The bug list is long.

• Hosszú a hibajegyzék.
  More emphasis on long: The bug list is long / It’s long, the bug list.

So both can be correct, but the first one is the more neutral, straightforward version.

A rough pronunciation guide is:

• A ≈ short aw
• hibajegyzék ≈ HEE-baw-yegyz-ayk
• hosszú ≈ HOS-soo

A few important spelling/pronunciation points:

• j is pronounced like English y
• sz is pronounced like English s
• plain s is pronounced like English sh
• é is a long vowel, roughly like ay in say, but purer
• ú is a long oo
• the accents in é and ú matter: they show long vowels

So hosszú has a long final vowel, not a short one.

It is in the nominative singular form, which is the basic dictionary form.

Here it functions as the subject of the sentence:

• A hibajegyzék = the bug list
• hosszú = is long

Hungarian often adds endings to nouns for different cases, but here there is no extra case ending because the noun is simply the subject.

Hosszú usually means long, and it can be used in several related senses, depending on context:

• physical length: a hosszú út = the long road
• duration: hosszú idő = a long time
• something lengthy: hosszú lista = a long list

In A hibajegyzék hosszú, it most naturally means the list is long/lengthy, meaning it has a lot in it or takes a long form.