L'interprete di conferenza controlla il glossario.

Because lo or la becomes l' before a word starting with a vowel.

• lo interprete → l'interprete
• la interprete → l'interprete

This means l'interprete can refer to either a masculine or a feminine singular noun. You usually understand the gender from context, or from an adjective/article elsewhere in the sentence.

It can be either masculine or feminine.

• l'interprete = the interpreter (male or female)
• un interprete = a male interpreter
• un'interprete = a female interpreter

So interprete is one of those Italian nouns whose form stays the same, while the article helps show gender.

Di conferenza means of conference or more naturally in English, conference as a type.

So:

• interprete di conferenza = conference interpreter

Italian often uses di + noun where English uses a noun as an adjective.

Compare:

• sala riunioni = meeting room
• scarpe da tennis = tennis shoes
• interprete di conferenza = conference interpreter

Italian uses definite articles more often than English.

Here, il glossario means the glossary. In many contexts, Italian prefers the article where English might sometimes omit it.

• controlla il glossario = checks the glossary

The article il is used because:

• glossario is singular
• it is masculine
• it starts with a consonant

Controlla is the third person singular of the verb controllare in the present indicative.

Conjugation:

• io controllo = I check
• tu controlli = you check
• lui/lei controlla = he/she checks

So in this sentence:

• L'interprete di conferenza controlla il glossario.
• The conference interpreter checks the glossary.

No, and this is a very important point.

In Italian, controllare often means:

• to check
• to inspect
• to verify
• sometimes to monitor

It does not usually mean to control in the sense of to dominate or to command.

So here controlla il glossario means:

• checks the glossary
• not controls the glossary

This is a common false friend for English speakers.

This is the most neutral Italian word order:

subject + verb + object

• L'interprete di conferenza = subject
• controlla = verb
• il glossario = object

Italian word order is often flexible, but this version sounds natural and standard.

Possible changes are sometimes possible for emphasis, for example:

• Il glossario lo controlla l'interprete di conferenza.

But that is much less neutral and more marked. For learners, the original order is the best model.

A helpful approximate pronunciation is:

leen-ter-pre-te dee kon-fe-REN-tsa kon-TROL-la eel glo-SSA-rio

A few useful notes:

• gli does not appear here, so glossario starts with a normal gl sound, not the special gli sound.
• zz is not in this sentence either, but conferenza has -enza, pronounced roughly -EN-tsa.
• controlla has double ll, so the consonant is held a bit longer than in English.
• Stress is usually:
  • intèrprete
  • conferènza
  • contròlla
  • glossàrio

Usually interprete di conferenza is the standard expression for the profession or specialization: conference interpreter.

Interprete della conferenza would more likely mean:

• the interpreter for the conference
• the specific interpreter associated with that event

So the difference is roughly:

• interprete di conferenza = conference interpreter as a type/job
• interprete della conferenza = the interpreter of/for the conference, a specific situation

The plural would be:

Gli interpreti di conferenza controllano il glossario.

Changes:

• l'interprete → gli interpreti
• controlla → controllano
• il glossario can stay singular if they are checking one glossary

If they are checking multiple glossaries:

Gli interpreti di conferenza controllano i glossari.

Because l'interprete can be masculine or feminine, you often need the article or context to make gender clearer.

For example:

• Un'interprete di conferenza controlla il glossario. = A female conference interpreter checks the glossary.
• L'interprete di conferenza è preparata. = The conference interpreter is prepared.
  Here preparata shows the interpreter is female.

In your original sentence, l'interprete by itself does not clearly show gender.

Because il glossario is the direct object of controlla.

The structure is:

• someone checks something

So Italian, like English, does not use a preposition here:

• controlla il glossario
• checks the glossary

You would only add a preposition if the verb required one, but controllare takes a direct object.

Not exactly.

• glossario = glossary, usually a list of specialized terms and their meanings
• dizionario = dictionary

So in a professional language context, glossario often refers to a terminology list, which makes very good sense with interprete di conferenza.