У этой рубашки слишком длинный рукав.

For ordinary possession, Russian usually prefers у + genitive rather than иметь.

So У этой рубашки слишком длинный рукав literally works like At this shirt, the sleeve is too long, but the natural English meaning is This shirt has a sleeve that is too long.

Using иметь here would sound much less natural in everyday speech. Russian normally uses иметь in more formal, abstract, or specialized contexts.

Both are in the genitive singular:

• эта → этой
• рубашка → рубашки

That is because the preposition у requires the genitive case.

So:

• у этой рубашки = of / at this shirt, in the Russian possession pattern

Russian often leaves out the present-tense verb to be.

So where English says:

• The sleeve is too long
• This shirt has a sleeve that is too long

Russian can simply say:

• У этой рубашки слишком длинный рукав

There is no present-tense есть here. That omission is normal.

Yes, and this is something learners often notice.

The singular рукав can be used when talking about the sleeve as a feature of the shirt in a general sense, or when one sleeve is being treated as representative.

But if you clearly mean both sleeves, Russian often uses the plural:

• У этой рубашки слишком длинные рукава.

That may sound more natural in many real-life situations if both sleeves are too long.

So the singular is possible, but the plural is also very common depending on what exactly the speaker wants to emphasize.

Рукав is nominative singular.

In this sentence, it is the noun being described as too long, so it behaves like the grammatical subject of the statement:

• рукав = sleeve
• длинный = long

Russian is essentially saying:

• The sleeve is too long
• with у этой рубашки added to show which shirt we are talking about

That is why рукав is not in the genitive with рубашки.

Because it agrees with рукав.

Рукав is:

• masculine
• singular
• nominative

So the adjective must also be:

• masculine
• singular
• nominative

That gives:

• длинный рукав

If the noun were plural, the adjective would also change:

• длинные рукава

Russian adjectives have long forms and, for some adjectives, short forms.

Here, the long form длинный is the normal, natural choice.
A sentence like рукав длинен sounds literary, old-fashioned, or unusually formal in modern speech.

So in everyday Russian:

• рукав слишком длинный = natural
• рукав слишком длинен = possible in theory, but not what learners should normally say

No.

• слишком = too, excessively
• очень = very

So:

• слишком длинный = too long
• очень длинный = very long

That difference is important.
Слишком implies a problem or excess.

Yes. Russian word order is flexible, and changing it usually changes the focus or emphasis, not the basic meaning.

For example:

• У этой рубашки слишком длинный рукав.
  Neutral word order.

• У этой рубашки рукав слишком длинный.
  Puts a little more focus on рукав first, then comments on it.

• Слишком длинный рукав у этой рубашки.
  More emphasis on too long.

For learners, the original version is a good neutral model.

Yes. That means This shirt has sleeves that are too long.

In many everyday situations, that plural version may actually be the clearest choice, because shirts normally have two sleeves.

So the difference is roughly:

• слишком длинный рукав = the sleeve is too long / a sleeve is too long / the sleeve length is too long
• слишком длинные рукава = the sleeves are too long

Both are grammatical; the best one depends on the situation.

Because Russian needs a clear structure showing what belongs to what.

If you say:

• эта рубашка = this shirt
• длинный рукав = a long sleeve

you still need a natural way to connect them. Russian commonly does that with the possession pattern:

• у этой рубашки ...

So instead of trying to build the sentence the same way English does, Russian uses its own normal pattern:

• У этой рубашки слишком длинный рукав.

That is one of the big things English speakers need to get used to in Russian: the grammar of possession often works very differently.