Quando a reunião terminar, eu vou voltar a estudar português.

Because after quando when it refers to a future event, Portuguese usually uses the future subjunctive.

So:

• Quando a reunião termina = when the meeting ends / whenever the meeting ends in a habitual or general sense
• Quando a reunião terminar = when the meeting ends in the future, on this specific occasion

In English, we often use the present after when for future meaning, but Portuguese often uses the future subjunctive instead.

It is the future subjunctive of terminar.

For regular verbs ending in -ar, the form often looks the same as the infinitive in some persons:

• eu terminar
• você/ele/ela terminar
• nós terminarmos
• vocês/eles/elas terminarem

So in this sentence, a reunião terminar means the meeting ends / has ended, referring to the future.

Because the action has not happened yet. The sentence is talking about a future event whose completion will come before the next action.

A good rule:

• Use quando + indicative for things that are habitual, repeated, or already known as facts.
• Use quando + future subjunctive for future situations.

Examples:

• Quando eu tenho tempo, estudo português. = When I have time, I study Portuguese.
• Quando eu tiver tempo, estudarei português. = When I have time in the future, I will study Portuguese.

Because the sentence begins with a dependent time clause:

• Quando a reunião terminar = When the meeting ends

Then comes the main clause:

• eu vou voltar a estudar português = I’m going to go back to studying Portuguese

In Portuguese, as in English, it is very common to put a comma after an introductory clause like this.

Both are possible, but they feel a little different.

• eu vou voltar a estudar português = I’m going to go back to studying Portuguese
• voltarei a estudar português = I will go back to studying Portuguese

In Brazilian Portuguese, ir + infinitive is extremely common in everyday speech and often sounds more natural and conversational than the simple future.

So this sentence sounds very normal and natural in Brazil.

Voltar a + infinitive means to do something again or to go back to doing something.

So:

• voltar a estudar = to study again / to go back to studying
• voltar a trabalhar = to go back to working
• voltar a dormir = to fall asleep again / sleep again

In this sentence, it suggests the speaker had been studying Portuguese before, stopped for some reason, and will resume after the meeting.

Because voltar often connects to another verb with the preposition a.

Pattern:

• voltar a + infinitive

Examples:

• voltar a ler
• voltar a falar
• voltar a tentar

You should learn it as a fixed structure:

• voltar a fazer algo = to do something again

No, it is optional.

Portuguese often drops subject pronouns because the verb form already shows the subject:

• vou voltar a estudar português
• eu vou voltar a estudar português

Both are correct.

Including eu can add:

• emphasis
• clarity
• contrast

In everyday Brazilian Portuguese, people often include subject pronouns more than in European Portuguese, but they are still frequently omitted when the meaning is clear.

Yes. Reunião is a feminine noun, so it takes the feminine article a:

• a reunião = the meeting

Other examples:

• a aula
• a conversa
• a decisão

You usually need to learn the gender of each noun along with the noun itself.

After estudar, the language name is often used without the article:

• estudar português
• estudar inglês
• estudar espanhol

That is the most common pattern here.

You may sometimes see articles with language names in other contexts, but after estudar, leaving the article out is very normal.

Yes. Terminar and acabar can both work here.

• Quando a reunião terminar...
• Quando a reunião acabar...

Both mean when the meeting ends.

A small nuance:

• terminar can sound a bit more neutral or formal
• acabar is also very common and natural in speech

In most everyday situations, either one would be understood perfectly.

Yes, that is also correct.

• Quando a reunião terminar... = When the meeting ends...
• Depois que a reunião terminar... = After the meeting ends...

The difference is small:

• quando focuses on the time point
• depois que emphasizes sequence: first the meeting ends, then the studying resumes

Both are natural.

The structure is:

Quando + subject + future subjunctive, subject + ir + infinitive + voltar a + infinitive + object

Broken down:

• Quando = when
• a reunião = the meeting
• terminar = ends
• eu = I
• vou voltar = am going to go back
• a estudar = to studying / to study again
• português = Portuguese

So the sentence is built from:

1. a time clause
2. a main clause

That pattern is very common in Portuguese.