يقصر الخياط الكم، في حين أنه يطيل الحاشية.

This is a very common Arabic sentence pattern: verb + subject + object.

So:

• يقصر = shortens
• الخياط = the tailor
• الكم = the sleeve

Together: يقصر الخياط الكم = The tailor shortens the sleeve.

Arabic can also say:

• الخياط يقصر الكم

That is also correct, but it feels more like The tailor shortens the sleeve with a little more focus on the tailor as the topic. The version in your sentence is a very normal verbal sentence in MSA.

Here it means shortens.

Without vowel marks, يقصر can be ambiguous. It could represent different pronunciations and meanings. In this sentence, because it takes a direct object (الكم), it is understood as:

• يُقَصِّرُ = he shortens

This is from Form II, which often gives a causative or intensive sense.

By contrast, يَقْصُرُ can mean is short or falls short, which would not fit this sentence well.

So the fully vowelled reading here is:

• يُقَصِّرُ الخَيَّاطُ الكُمَّ

الكم is the direct object of the verb يقصر.

The structure is:

• يقصر = verb
• الخياط = subject
• الكم = direct object

So the tailor is the one doing the action, and the sleeve is what the action is being done to.

In full case endings, it would be:

• يُقَصِّرُ الخَيَّاطُ الكُمَّ

Here:

• الخياطُ is nominative because it is the subject
• الكمَّ is accusative because it is the direct object

In normal unvowelled writing, those endings are usually not shown.

في حين أنه means something like:

• while
• whereas
• while it is the case that
• at the same time that

In this sentence, it connects two contrasting or parallel actions:

• يقصر الخياط الكم
• في حين أنه يطيل الحاشية

So the meaning is roughly:

• The tailor shortens the sleeve, while he lengthens the hem.

This expression is quite common in formal or written Arabic.

Good question. أنه introduces a full clause after في حين in a very standard MSA way.

So:

• في حين أنه يطيل الحاشية

literally has the sense of:

• while it is the case that he lengthens the hem

The ـه in أنه refers back to الخياط.

Arabic often uses this kind of structure even when English would simply say while he lengthens...

You may also see shorter alternatives in Arabic, such as:

• في حين يطيل الحاشية
• بينما يطيل الحاشية

But في حين أنه is perfectly natural and slightly more explicit.

Because it refers back to الخياط, which is a singular masculine noun.

• الخياط = the tailor
• so the matching pronoun is هو = he
• inside أنّ, this becomes أنه = that he

So أنه يطيل الحاشية means that he lengthens the hem, with he referring to the tailor.

If the subject were feminine, plural, or dual, the pronoun would change accordingly.

Because they are definite nouns:

• الخياط = the tailor
• الكم = the sleeve
• الحاشية = the hem / edge

Arabic uses الـ to mark definiteness, similar to the in English.

In this sentence, the nouns are definite because the speaker is talking about specific parts or a specific role in context, not just any tailor or any sleeve in a general abstract sense.

Yes.

يطيل means he lengthens and comes from the verb أطالَ.

So:

• يُطِيلُ = he lengthens

This is a transitive verb, so it can take a direct object:

• يطيل الحاشية = he lengthens the hem

It pairs neatly with يقصر in this sentence:

• يقصر = shortens
• يطيل = lengthens

So the sentence sets up a contrast between making one part shorter and another part longer.

In general, حاشية can mean margin, edge, border, or trim, depending on context.

In a tailoring or clothing context, الحاشية is naturally understood as something like:

• the hem
• the edge
• the border of the garment

So in this sentence, يطيل الحاشية means he is making the hem or edge longer.

Arabic often uses the singular when talking about a part of a garment in a general or contextual way.

So:

• الكم = the sleeve
• الحاشية = the hem

This does not necessarily mean only one sleeve exists; it just refers to the relevant part being altered. Arabic often leaves that to context.

If you specifically wanted the sleeves, you could say:

• الأكمام

But the singular is completely natural here.

Both are in the imperfect tense:

• يقصر
• يطيل

In MSA, the imperfect can express:

• present action
• habitual action
• general statements
• sometimes future, if another marker is added

Here it most naturally means a present or habitual action:

• The tailor shortens the sleeve and lengthens the hem
• or The tailor is shortening the sleeve while lengthening the hem, depending on context

Since Arabic does not have a separate is shortening form the way English does, context decides how to translate it best.

A fully vowelled version would be:

• يُقَصِّرُ الخَيَّاطُ الكُمَّ، في حينِ أَنَّهُ يُطِيلُ الحاشِيَةَ.

This shows several things clearly:

• يُقَصِّرُ = he shortens
• الخَيَّاطُ = the tailor, nominative subject
• الكُمَّ = the sleeve, accusative object
• في حينِ = while / whereas
• أَنَّهُ = that he
• يُطِيلُ = he lengthens
• الحاشِيَةَ = the hem, accusative object

Seeing the vowels can be very helpful, especially for a learner, because unvowelled Arabic leaves some forms ambiguous.