I am loath to say this is not English, but it is awkward because of the piling up of indefinite articles.

Careful: This sentence is typical of loser's sentences.

Punchy (but ambiguous): This is a typical loser's sentence.

Idiomatic: This sentence has a loser's ring to it. (Ring = sound.) This sentence has loser written all over it.

What I suppose you mean: This sentence is just about what you'd expect from a loser.

Note that the word-for-word translation of the Portuguese is good English: This sentence is typical of a loser.

no you haven't...

done!

sentence is still repeated ...

I made a mistake.

This sentence is typical of loser's sentences.

should be

This sentence is typical of losers' sentences.

Still bad.

How can that be? It's my sentence, and I even patched it?

What I tried to do is to make a grammatically correct English sentence that did not include the "an A of a B" construction. I failed to make an English sentence that is either natural or an accurate translation of "Essa frase é típica de um derrotado." (Actually, I wasn't even looking at that sentence; but that's where we should start.)

Since the result is neither a natural English sentence nor an accurate translation, it doesn't belong here.

The first thing we notice about the Portuguese is that it's a joke. It's meant to be funny and it is funny. An accurate translation should be funny too.

What makes it funny? What are the ideas of the sentence? There are three. (1) Sentence. The point here is that this sentence is being contributed to a collection of sentences, and it refers to itself. (2) Typical. An accurate translation need not include this word, but it should express the same idea. (3) Derrotado. I take it from you that this means loser. This is the heart of the joke.

When we put these three things together, we make a joke of the self-deprecating variety, because it implies that the owner-author is a loser.

Now how can we do all that in a natural English sentence?

Humor benefits from brevity; and with that in mind, my best translation is "Typical loser's sentence." Where's the verb? This is an example of an elliptical sentence: elliptical means something has been left out--here it's the verb. The pattern substitutes <adjective><noun> for "This <noun1> is an <adjective><noun1>." Short, funny, natural, good English: good translation.

The original sentence is not as short as our translation. It gains some of its humor by delaying the appearance of derrotado--and so the joke--to the very end. We can achieve the same effect by expressing the idea of "typical" in different words: "This sentence is just about what you'd expect from a loser." That's my second best translation.

We require: (1) grammatically correct, (2) natural, (3) same meaning, (4) same effect.