لو فيه خصم على القميص، انا هختاره بدل البنطلون.

لو means if. It introduces a condition:

• لو فيه خصم... = If there is a discount...

In Egyptian Arabic, لو is the normal everyday word for if in sentences like this.

فيه here means there is / there are.

So:

• فيه خصم = there is a discount

This is a very common Egyptian structure.
Be careful, because في by itself often means in, while فيه can mean there is.

خصم means discount.

In shopping language:

• خصم = discount
• تخفيض = reduction / sale markdown

Both are used, but خصم is very common in everyday speech.

In Arabic, the usual way to say a discount on something is with على:

• خصم على القميص = a discount on the shirt

This is just a normal preposition choice in Arabic. It does not have to match English exactly.

Yes, هختاره already tells you the subject is I.

So أنا is not strictly necessary. It is often added for:

• emphasis
• clarity
• contrast

So أنا هختاره can feel a bit like I’ll choose it.

هختاره can be broken down like this:

• هـ = future marker, like will / going to
• اختار / أختار = choose / I choose
• ـه = it / him attached object pronoun

So:

• هختاره = I will choose it

In this sentence, it refers to القميص.

In Egyptian Arabic, بـ is often used with the present tense, especially for habitual or regular actions:

• باختاره = I choose it / I usually choose it

But for the future, Egyptian commonly uses هـ or حـ instead:

• هختاره = I will choose it

So the future marker replaces the present بـ here.

The ـه means it and refers to القميص (the shirt).

Arabic often attaches object pronouns directly to the verb:

• هختار = I will choose
• هختاره = I will choose it

Since القميص is grammatically masculine singular, ـه is the correct pronoun.

بدل means instead of or in place of.

So:

• بدل البنطلون = instead of the pants / trousers

It means the speaker would choose the shirt, not the pants.

In Egyptian Arabic, بدل can be followed directly by a noun:

• بدل البنطلون = instead of the pants

That is normal and natural.
You may sometimes hear longer expressions in other contexts, but here بدل + noun is the straightforward everyday pattern.

That is just a vocabulary difference between the two languages.

In Arabic:

• بنطلون is grammatically singular

But in English, the natural translation is often pants or trousers, which look plural.

So even though English uses a plural-looking word, Arabic treats it as one item.

It can be rearranged.

The given sentence starts with the condition, which is very natural:

• لو فيه خصم على القميص، انا هختاره بدل البنطلون.

You could also say something like:

• أنا هختاره بدل البنطلون لو فيه خصم على القميص.

Both are understandable. Starting with لو makes the condition come first and gives it more focus.

A rough pronunciation guide would be:

law fīh khasm ʿala l-ʔamīṣ, ana hakhtāro badal il-banṭalōn

A few notes:

• لو = law
• فيه = fīh
• خصم = khasm
• القميص in Egyptian is often pronounced with a glottal stop instead of q, so roughly el-ʔamīṣ
• البنطلون = el-banṭalōn

Exact pronunciation will vary a bit by speaker, but this is a good general guide.

Yes, it sounds natural and clear.

It expresses a simple shopping decision:

• If the shirt is discounted, I’ll choose it instead of the pants.

A native speaker might also phrase it in slightly different ways, but the sentence you have is perfectly understandable and natural for everyday Egyptian Arabic.