Quando o farol ficar verde, a gente vai atravessar a rua.

Because ficar often means to become or to end up in a state.

So:

• ficar verde = to turn green / to become green
• estar verde = to be green
• ser verde = to be green in a more permanent or defining sense

With a traffic light, the idea is a change of state, so Portuguese uses ficar very naturally:

• O farol ficou verde. = The light turned green.
• Quando o farol ficar verde... = When the light turns green...

Here ficar is in the future subjunctive, not the present indicative.

Portuguese often uses the future subjunctive after words like:

• quando = when
• se = if
• assim que = as soon as
• logo que = as soon as

when the action refers to a future event that has not happened yet.

So:

• Quando o farol fica verde... would sound like a habitual or general statement: When the light turns green...
• Quando o farol ficar verde... means When the light turns green (in the future, this time)...

This is one of the most important patterns in Portuguese.

The future subjunctive is a tense/mood Portuguese uses for possible or expected future situations, especially in subordinate clauses.

It is very common in everyday Portuguese, much more than anything similar in English, because English usually just uses the present:

• When it turns green, we’ll cross the street.

In Portuguese, that same idea becomes:

• Quando ficar verde, vamos atravessar.

Other examples:

• Se eu tiver tempo, eu vou. = If I have time, I’ll go.
• Quando você chegar, me liga. = When you arrive, call me.
• Assim que ele souber, ele avisa. = As soon as he finds out, he’ll let us know.

A gente is a very common Brazilian Portuguese way to say we in everyday speech.

Even though it means we, it is grammatically treated as third-person singular, so the verb is singular:

• A gente vai = we go / we are going
• A gente quer = we want
• A gente atravessa = we cross

Compare:

• Nós vamos atravessar a rua. = We are going to cross the street.
• A gente vai atravessar a rua. = We are going to cross the street.

Both are correct, but a gente is usually more common in spoken Brazilian Portuguese.

A gente is neutral-to-informal and extremely common in Brazil, especially in conversation.

Use it freely in:

• speaking
• texting
• casual writing
• most everyday situations

In more formal writing, people may prefer nós.

So:

• A gente vai atravessar a rua. = very natural in speech
• Nós vamos atravessar a rua. = also correct, slightly more formal or careful

Because in Brazilian Portuguese, the structure ir + infinitive is very common for future meaning.

So:

• vai atravessar = is going to cross / will cross
• atravessará = will cross

Both are correct, but vai atravessar sounds more natural in everyday spoken Brazilian Portuguese.

Compare:

• A gente vai atravessar a rua. = very common, conversational
• A gente atravessará a rua. = more formal, less common in speech

Good question. Farol can mean different things depending on context.

In Brazilian Portuguese, it can mean:

• lighthouse
• headlight
• traffic light

In this sentence, because of ficar verde, it clearly means traffic light.

In Brazil, farol is a very common everyday word for traffic light, though you may also hear:

• semáforo = traffic light

So both can work, but farol is very natural in Brazil.

Portuguese often uses the definite article where English does not.

So:

• atravessar a rua = cross the street
• entrar no carro = get in the car
• fechar a porta = close the door

Even when English might omit the article in some contexts, Portuguese usually keeps it.

Not in this exact way for standard usage.

For traffic lights, the most natural expression is:

• o farol ficar verde
• o sinal abrir in some regional or colloquial usage

But abrir literally means to open, so it is not the default verb with farol in this context.

If you want the safest, most widely understandable option, use:

• Quando o farol ficar verde...

Yes, but the meaning shifts slightly.

• Quando o farol ficar verde = when the light turns green
• Quando o farol estiver verde = when the light is green

The first focuses on the change.
The second focuses on the state.

In practice, both can work in many situations, but ficar verde is especially natural if you are waiting for the light to change.

Yes.

These are both correct:

• Quando o farol ficar verde, a gente vai atravessar a rua.
• Quando o farol ficar verde, vamos atravessar a rua.

The second version drops the explicit subject and uses the first-person plural verb vamos.

They both mean we’re going to cross the street, but:

• a gente vai = very common in spoken Brazilian Portuguese
• vamos = also very common and slightly more concise

A simple approximate pronunciation is:

KWAN-doo oo fah-ROU fee-KAR VEHJ-dee, ah ZHEN-chee VAI ah-trah-veh-SAIR ah HOO-ah

A few notes:

• quando: the qu sounds like kw
• farol: final l often sounds like w in Brazilian Portuguese
• verde: the d before e often sounds like j in many Brazilian accents, so it can sound like verji
• a gente: the g sounds like the s in measure
• rua: two vowel sounds, roughly roo-ah

It is very natural Brazilian Portuguese.

Why it sounds natural:

• farol for traffic light is common
• ficar verde is the usual way to say turn green
• a gente is very common in speech
• vai atravessar is a natural future form in conversation

So this is the kind of sentence you could really hear on the street in Brazil.