Η στίξη σε αυτό το κείμενο δεν είναι σωστή.

A word-by-word breakdown is:

• Η = the (feminine singular)
• στίξη = punctuation
• σε = in / on / at
• αυτό = this
• το = the (neuter singular)
• κείμενο = text
• δεν = not
• είναι = is
• σωστή = correct

A more natural English rendering is The punctuation in this text is not correct.

Η is the feminine singular definite article, meaning the.

Greek nouns have grammatical gender, and στίξη is a feminine noun, so it takes η in the nominative singular:

• η στίξη = the punctuation

Unlike English, Greek uses articles very regularly, so leaving it out would often sound incomplete or less natural in a sentence like this.

Because it agrees with στίξη.

In Greek, adjectives must agree with the noun they describe in:

• gender
• number
• case

Since στίξη is:

• feminine
• singular
• nominative

the adjective must also be feminine singular nominative:

• σωστός = masculine
• σωστή = feminine
• σωστό = neuter

So:

• Η στίξη ... δεν είναι σωστή = The punctuation ... is not correct

In Greek, demonstratives like αυτός / αυτή / αυτό usually appear together with the definite article.

So this text is:

• αυτό το κείμενο

not normally just:

• αυτό κείμενο

Here:

• αυτό = this
• το = the
• κείμενο = text

This is a very common Greek pattern:

• αυτό το βιβλίο = this book
• αυτή η μέρα = this day
• αυτό το κείμενο = this text

It is in the accusative case.

After the preposition σε (in / on / at / to), Greek normally uses the accusative:

• σε αυτό το κείμενο = in this text

You can see this especially in the article and noun:

• nominative: το κείμενο
• accusative: το κείμενο

In this noun, nominative and accusative look the same, which is very common for neuter nouns. So the case is not obvious from the form alone, but grammatically it is accusative because of σε.

Δεν is the standard negation used with verbs in ordinary statements.

So:

• είναι = is
• δεν είναι = is not

Greek mainly uses:

• δεν before verbs in statements
• μη(ν) in other environments, such as commands or subjunctive-related structures

In this sentence, it is a simple statement, so δεν is the correct negative particle.

Yes, in a sentence like this Greek normally uses the verb είμαι (to be), just like English does here.

So:

• Η στίξη ... είναι σωστή = The punctuation ... is correct
• Η στίξη ... δεν είναι σωστή = The punctuation ... is not correct

Greek can sometimes omit forms of to be in very informal contexts, headlines, notes, or special structures, but in a normal full sentence like this, είναι is expected.

The given word order is very natural:

• Η στίξη σε αυτό το κείμενο δεν είναι σωστή.

Greek word order is more flexible than English, because case endings help show grammatical relationships. So other orders are possible, depending on emphasis.

For example:

• Η στίξη δεν είναι σωστή σε αυτό το κείμενο.
• Σε αυτό το κείμενο, η στίξη δεν είναι σωστή.

These are all understandable, but the original version sounds neutral and natural.

A rough pronunciation guide is:

• Η στίξη σε αυτό το κείμενο δεν είναι σωστή
• ee STIK-see se af-TO to KEE-me-no then EE-ne so-STEE

A few notes:

• η sounds like ee
• ξ sounds like ks
• αι in είναι sounds like e
• ση / σης / στη type endings often have a clear s sound, not a sh sound

The stress marks show which syllable is stressed:

• στίξη
• αυτό
• κείμενο
• είναι
• σωστή

Yes, στίξη is generally used much like English punctuation: as a singular, abstract noun.

So Greek says:

• Η στίξη είναι σωστή = The punctuation is correct
• Η στίξη δεν είναι σωστή = The punctuation is not correct

Even though punctuation consists of many marks, the noun itself is singular, just as in English.

Yes. σωστός / σωστή / σωστό can mean:

• correct
• right
• proper

The best translation depends on context. In this sentence, correct is the most natural choice:

• Η στίξη ... δεν είναι σωστή = The punctuation ... is not correct

But in other contexts:

• Η απάντηση είναι σωστή = The answer is correct
• Δεν είναι σωστό = It is not right / proper

The accent marks show which syllable is stressed.

For a learner, they are very important because stress in Greek is phonemic: putting stress on the wrong syllable can sound unnatural or even create confusion.

For example:

• στίξη → stress on στί-
• αυτό → stress on -τό
• κείμενο → stress on κεί-
• είναι → stress on εί-
• σωστή → stress on -στή

So when learning Greek vocabulary, it is best to memorize the word together with its accent.