Exemplarul indisponibil apare în catalog.

Because Romanian usually puts the definite article at the end of the noun.

• exemplar = a copy / an item
• exemplarul = the copy / the item

So the English word the is not separate here; it is attached to the noun as -ul.

Because the normal Romanian order is noun + adjective.

So:

• exemplarul indisponibil = the unavailable copy

That is the most neutral, standard order. Romanian can put the adjective before the noun for emphasis or style, but that is less neutral.

It already matches the noun correctly. Exemplarul is masculine singular, and the matching adjective form is indisponibil.

Compare:

• masculine singular: indisponibil
• feminine singular: indisponibilă
• masculine plural: indisponibili
• feminine/neuter plural: indisponibile

So in this sentence, indisponibil is the correct agreement form.

Apare is the 3rd person singular present tense of a apărea = to appear.

Here it agrees with the singular subject exemplarul indisponibil. In context, apare can mean not only appears, but also something like shows up or is listed.

Because Romanian often leaves subject pronouns out when they are not necessary. The subject is already stated: exemplarul indisponibil.

So Romanian does not need an extra pronoun like English it. This is very common.

Romanian article use does not always match English article use word for word. In a sentence like this, în catalog is a natural way to say that something appears or is listed in the catalog, especially when the catalog is understood from context.

If you want to identify the catalog more specifically, you would usually make that explicit, for example:

• în catalogul bibliotecii = in the library’s catalog
• în catalogul online = in the online catalog

No. Exemplarul indisponibil apare în catalog is the neutral order:

• subject: Exemplarul indisponibil
• verb: apare
• prepositional phrase: în catalog

But Romanian can change the order for emphasis. For example:

• În catalog apare exemplarul indisponibil

This puts more focus on în catalog.

A natural plural version would be:

Exemplarele indisponibile apar în catalog.

Changes:

• exemplarul → exemplarele
• indisponibil → indisponibile
• apare → apar

So the noun, adjective, and verb all change to match the plural subject.

A rough pronunciation guide is:

eg-zem-PLA-rul in-dis-po-ni-BIL a-PA-re în kata-LOG

A few useful notes:

• x in exemplarul sounds like gz here.
• ă in apare is a short central vowel, somewhat like uh.
• î in în is a specifically Romanian sound with no exact English equivalent.
• The main stresses are roughly on -pla-, -bil, -pa-, and -log.