В этом предложении не хватает двоеточия.

Because этом has to agree with предложении.

• The dictionary form is предложение = sentence
• It is a neuter noun
• After в in the meaning in, Russian usually uses the prepositional case

So:

• это предложение = this sentence nominative
• в этом предложении = in this sentence prepositional

The form этой would be feminine, and этого would be masculine/neuter genitive, so neither fits here.

Because here в means in, not into.

Russian uses different cases depending on whether you mean:

• location: in/inside something → usually prepositional
• direction/motion into something → usually accusative

So:

• в этом предложении = in this sentence
• в это предложение = into this sentence

Since the sentence is talking about something missing in the sentence, Russian uses the prepositional case: в этом предложении.

This is the prepositional singular form.

The noun предложение belongs to a common neuter pattern ending in -ие. Nouns of this type often change like this:

• nominative singular: предложение
• prepositional singular: о предложении, в предложении

So in в этом предложении, both the pronoun and the noun are in the prepositional case.

A useful pattern to remember:

• здание → в здании
• упражнение → в упражнении
• предложение → в предложении

Не хватает means something like:

• is lacking
• is missing
• there isn’t enough of

The verb is хватать / хватить, which often has the idea of being sufficient or being enough.

So:

• Мне хватает времени = I have enough time
• Мне не хватает времени = I don’t have enough time / I’m short of time

In your sentence:

• В этом предложении не хватает двоеточия
  = This sentence is missing a colon
  literally: In this sentence, there is not enough of a colon / a colon is lacking

Because this is an impersonal construction.

Russian often uses хватает / не хватает in the fixed third-person singular form when talking about whether something is sufficient or missing.

So even though English might say:

• A colon is missing
• Two words are missing

Russian still often keeps:

• не хватает двоеточия
• не хватает двух слов

The verb does not have to agree with the thing that is missing in the way an English verb often would.

Because не хватает usually takes the genitive case for the thing that is lacking.

The dictionary form is:

• двоеточие = colon

But after не хватает, it becomes:

• двоеточия = genitive singular

Compare:

• Есть двоеточие = There is a colon
• Нет двоеточия = There is no colon
• Не хватает двоеточия = A colon is missing

This genitive after expressions of absence or insufficiency is very common in Russian.

Двоеточие is the punctuation mark :, called a colon in English.

Other useful punctuation words:

• запятая = comma
• точка = period / full stop
• точка с запятой = semicolon
• тире = dash
• вопросительный знак = question mark
• восклицательный знак = exclamation mark

So не хватает двоеточия specifically means a colon is missing, not some other punctuation mark.

Yes, absolutely.

Both are natural, but the nuance is a little different:

• В этом предложении нет двоеточия = There is no colon in this sentence
• В этом предложении не хватает двоеточия = This sentence is missing a colon

The first one states absence more neutrally.
The second one suggests that the colon should be there, but isn’t.

So if you are correcting punctuation, не хватает двоеточия is especially appropriate.

There is no normal subject in the Russian sentence. It is an impersonal way of speaking.

English often prefers something like:

• This sentence is missing a colon

Russian often expresses the same idea as:

• In this sentence, a colon is lacking

So the structure is not really X misses Y, but more like Y is lacking in X.

That is why the sentence begins with the location:

• В этом предложении = in this sentence

And then gives the impersonal predicate:

• не хватает = is lacking / is missing

Yes. Russian word order is flexible, although the original order is very natural.

Original:

• В этом предложении не хватает двоеточия.

Possible variations:

• Двоеточия не хватает в этом предложении.
• Не хватает двоеточия в этом предложении.

These alternatives may sound more emphatic or stylistically marked depending on context.

The original version is the most straightforward for a neutral statement:

• first the setting: in this sentence
• then the main point: a colon is missing

The stress is on то:

• двоето́чие

A rough pronunciation guide for an English speaker could be:

• dvah-ye-TOH-chee-ye

Breakdown:

• двое- sounds roughly like dvoye-
• -то́- is stressed
• -чие sounds like chee-ye

If you want the full sentence with stress marks:

• В э́том предложе́нии не хвата́ет двоето́чия.

It can be used for both.

Physical or concrete things:

• В тексте не хватает запятой. = The text is missing a comma.
• На столе не хватает одной книги. = One book is missing from the table.

Abstract things:

• Мне не хватает опыта. = I lack experience.
• Ему не хватает терпения. = He lacks patience.
• Нам не хватает времени. = We don’t have enough time.

So in your sentence, it is being used for a concrete thing: a punctuation mark.