Se te enganares na vírgula, a frase fica confusa.

Because after se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation.

So:

• se te enganares = if you make a mistake / if you happen to make a mistake
• se te enganas would usually mean if you are mistaken or sound less natural here

This is a very common pattern in Portuguese:

• Se fores = if you go
• Se tiveres = if you have
• Se puderes = if you can
• Se te enganares = if you make a mistake

For learners, this is one of the most important things to notice in conditional sentences in Portuguese.

Enganares is the future subjunctive form of the verb enganar(-se).

Here is the base verb:

• enganar = to deceive, to trick
• enganar-se = to be mistaken, to make a mistake

In this sentence, it is the tu form:

• (tu) enganares

So se te enganares literally works like:

• if you mistake yourself
• but naturally it means if you make a mistake

Because the verb here is enganar-se, a pronominal/reflexive verb.

• enganar = to deceive someone
• enganar-se = to be mistaken / to make a mistake

So:

• Tu enganas-te = you make a mistake / you are mistaken
• Se te enganares = if you make a mistake

The te is the pronoun for you in the tu form.

This is very common in Portuguese with verbs that are used with pronouns:

• lembrar-se = to remember
• esquecer-se = to forget
• enganar-se = to be mistaken

They are doing different jobs.

• Se here is not a pronoun. It is the conjunction if.
• Te is the object/reflexive pronoun linked to enganar-se.

So:

• Se = if
• te = yourself / you

That means:

• Se te enganares... = If you make a mistake...

This is a very common source of confusion because se can mean different things in Portuguese, but in this sentence it simply means if.

Na is the contraction of:

• em
  • a = na

So:

• na vírgula = in/on the comma

In natural English, we would usually say:

• with the comma
• about the comma
• in the comma placement

But Portuguese often uses em in places where English uses a different preposition.

Here, enganar-se na vírgula means making a mistake with the comma or in the use of the comma.

Literally, yes, it looks like to be mistaken in the comma, but that is not how you should translate it into natural English.

A better natural meaning is:

• to make a mistake with the comma
• to get the comma wrong

Portuguese and English often package these ideas differently. It is better to learn this as an idiomatic pattern rather than word-for-word.

Portuguese often uses the definite article more than English does.

So:

• a frase = the sentence

Even when English might say the sentence or sometimes just speak more generally, Portuguese frequently keeps the article.

This happens a lot:

• O João chegou. = João arrived.
• A Maria saiu. = Maria left.
• A frase fica confusa. = The sentence becomes confusing.

In this sentence, a frase refers to the sentence being discussed, so the article is completely natural.

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

So:

• a frase fica confusa = the sentence becomes confusing / ends up confusing

If you said:

• a frase é confusa

that would mean the sentence is confusing, more as a general description.

Here, the idea is that the sentence becomes confusing because of the comma mistake, so fica is the better choice.

Portuguese often uses the present tense in the result clause to express a general consequence.

So:

• Se te enganares na vírgula, a frase fica confusa.

means something like:

• If you make a mistake with the comma, the sentence becomes confusing.

This sounds like a general rule or habitual truth.

You could sometimes see a future form in other contexts, but fica is very natural here because it states the consequence as something that normally happens.

It works in European Portuguese, and the structure is fully normal there.

A learner of Portugal Portuguese should especially notice:

• the use of the future subjunctive after se
• the use of the clitic pronoun te
• the common article usage in a frase
• the natural use of ficar for become

The sentence would also be understandable in Brazilian Portuguese, but your target as a Portugal learner should be to get comfortable with this kind of structure, because it is very standard in European Portuguese.

The structure is:

• Se te enganares na vírgula, = if you make a mistake with the comma
• a frase fica confusa. = the sentence becomes confusing

So the pattern is:

• Se + future subjunctive clause, main clause

This is one of the most useful sentence frames in Portuguese:

• Se tiveres tempo, liga-me. = If you have time, call me.
• Se fores cedo, apanhas o comboio. = If you go early, you catch the train.
• Se te enganares na vírgula, a frase fica confusa. = If you make a mistake with the comma, the sentence becomes confusing.

Yes. That is a very natural English translation.

Possible natural translations include:

• If you get the comma wrong, the sentence becomes confusing.
• If you make a mistake with the comma, the sentence becomes confusing.
• If you misuse the comma, the sentence becomes confusing.

So even though the Portuguese structure is different, get the comma wrong is an excellent way to understand it naturally in English.