Tu te plains souvent quand il faut faire la queue.

Because the verb is se plaindre, which is a pronominal (or reflexive-type) verb in French. That means it normally uses a reflexive pronoun:

• je me plains
• tu te plains
• il/elle se plaint

So te is not optional here. With this verb, se plaindre means to complain.

Also, plaindre by itself exists, but it means something different: to pity or to feel sorry for someone.

• Je plains Paul = I pity Paul.
• Je me plains = I complain.

Plains is the tu form of se plaindre in the present tense.

Conjugation:

• je me plains
• tu te plains
• il/elle se plaint
• nous nous plaignons
• vous vous plaignez
• ils/elles se plaignent

So tu te plains simply means you complain.

A useful thing to notice is that the singular forms sound very similar:

• plains
• plaint
• plaignent

But they are spelled differently.

It is pronounced approximately like tyu tə plɛ̃.

A few pronunciation points:

• tu has the French u sound, which does not exist exactly in English.
• te is often a light tuh sound in normal speech.
• plains has a nasal vowel at the end, so the -ns is not pronounced like in English. You do not say the final s.

So plains sounds roughly like plen with a nasal vowel, not like the English word plains.

In French, short adverbs of frequency like souvent often come after the conjugated verb:

• Tu te plains souvent = You often complain.

This is a very common position. English often puts often before the main verb, but French usually places souvent after the verb phrase.

Compare:

• Je mange souvent ici.
• Elle parle souvent trop vite.

So tu te plains souvent is the natural word order.

Here, quand means when.

It introduces a clause explaining under what circumstance the person complains:

• Tu te plains souvent = You often complain
• quand il faut faire la queue = when you have to queue / when you have to wait in line

So the whole sentence describes a repeated situation.

In il faut, the il does not refer to a person or thing. This is an impersonal expression.

Il faut means:

• it is necessary
• one must
• you have to
• it’s necessary to

So:

• il faut faire la queue = it is necessary to queue / you have to wait in line

This il is just a grammatical subject. It does not mean he here.

Very common examples:

• Il faut partir. = We have to leave.
• Il faut étudier. = You have to study.

French often uses the idiom faire la queue, literally to make the line, to mean:

• to queue
• to stand in line
• to wait in line

This is just the normal expression.

Examples:

• Nous faisons la queue au supermarché. = We’re waiting in line at the supermarket.
• J’ai horreur de faire la queue. = I hate queuing / waiting in line.

So even though English can use one verb (queue), French usually uses this fixed expression.

Usually yes, but there is one thing to know: in some contexts, queue can also mean tail, and in informal or vulgar language it can sometimes have another meaning. However, faire la queue is a completely standard everyday expression meaning to wait in line.

In normal situations like shops, airports, or ticket counters, there is no problem at all:

• On fait la queue depuis vingt minutes.

So learners should still use it confidently.

Yes. Lorsque also means when, and it is a bit more formal than quand.

• quand il faut faire la queue = normal, everyday
• lorsqu’il faut faire la queue = slightly more formal or written

In everyday speech, quand is more common.

Because falloir is followed directly by an infinitive:

• Il faut partir.
• Il faut attendre.
• Il faut faire la queue.

So you say il faut + infinitive, not il faut de + infinitive.

However, if you use a noun, the structure changes:

• Il faut du courage. = Courage is needed.
• Il faut de la patience. = Patience is needed.

But with a verb, no de:

• Il faut attendre.

Yes. If you are speaking to more than one person, or to one person formally, you would say:

Vous vous plaignez souvent quand il faut faire la queue.

Changes:

• tu te plains → vous vous plaignez

Everything else stays the same.

So the original sentence uses tu because it is informal and addressed to one person.

Often yes. If you say what someone is complaining about, you usually use de:

• Elle se plaint du bruit. = She complains about the noise.
• Je me plains de mon travail. = I complain about my job.

But in your sentence, the thing being complained about is expressed through the when-clause:

• Tu te plains souvent quand il faut faire la queue.

So there is no need for de here, because the sentence is not structured as complain about X, but rather complain when X happens.

Yes. Depending on context, it can be translated as:

• to queue
• to wait in line
• to stand in line
• to line up

For example:

• Les gens font la queue devant le cinéma. could be:
• People are queuing outside the cinema.
• People are standing in line outside the cinema.

So the best English translation depends on the situation, even though the French stays the same.