در آن فروشگاه یک شلوار تیره و یک پیراهن روشن دیدم.

Because Persian normally prefers Subject–Object–Verb order, unlike English, which usually uses Subject–Verb–Object.

So this sentence is structured roughly like:

در آن فروشگاه = in that store
یک شلوار تیره و یک پیراهن روشن = a dark pair of pants and a light shirt
دیدم = I saw

Literally, it is closer to:

In that store, a dark pair of pants and a light shirt saw-I.

That sounds strange in English, but it is normal in Persian.

Because the verb دیدم already tells you the subject.

دیدم means I saw. The -م ending shows first person singular, so Persian does not need to say من unless the speaker wants emphasis.

So:

دیدم = I saw
من دیدم = I saw / I was the one who saw

In neutral sentences, Persian often leaves the subject pronoun out.

در means in or inside.
آن means that.
فروشگاه means store/shop.

So در آن فروشگاه means in that store.

A useful point: آن comes before the noun, like English that store. There is no ezafe between آن and فروشگاه.

It can mean either, depending on context.

In this sentence:

یک شلوار تیره = a dark pair of pants
یک پیراهن روشن = a light shirt

Here یک is functioning like the English indefinite article a/an, although it still literally means one.

Persian has no separate word exactly like English a/an, so یک often does that job.

Because these are indefinite, newly introduced objects.

In Persian, را usually marks a specific direct object. Since یک شلوار تیره and یک پیراهن روشن mean a dark pair of pants and a light shirt, they are indefinite and nonspecific, so را is normally omitted.

So this is natural:

یک شلوار تیره و یک پیراهن روشن دیدم

If the objects were specific, را might appear:

آن شلوار تیره را دیدم = I saw that dark pair of pants

That is the normal order in Persian.

English says:

dark pants, light shirt

Persian says:

شلوار تیره = pants dark
پیراهن روشن = shirt light

So adjectives usually follow the noun they describe.

Yes, there is an ezafe in pronunciation, even though it is usually not written in ordinary Persian script.

So you pronounce them like:

shalvâr-e tire
pirâhan-e roshan

That little -e sound links the noun to the adjective.

So although the sentence is written:

شلوار تیره
پیراهن روشن

it is pronounced as if it were:

شلوارِ تیره
پیراهنِ روشن

No. Persian adjectives do not agree with nouns the way adjectives do in many European languages.

So تیره and روشن stay the same regardless of whether the noun is singular or plural, masculine or feminine.

That makes things simpler for learners:

پیراهن روشن = a light shirt
پیراهن‌های روشن = light shirts

The adjective itself does not change form.

Yes. In Persian, شلوار is normally used as a singular noun meaning pants/trousers as one item of clothing.

So:

یک شلوار = one pair of pants / a pair of trousers

Even though English uses a plural-looking form pants, Persian treats شلوار as a normal singular noun.

You sometimes can, but repeating یک is clearer and more balanced.

یک شلوار تیره و یک پیراهن روشن clearly means:

• a dark pair of pants
• and a light shirt

If you omit the second یک, the sentence may still be understood, but it sounds less neat and can be slightly less explicit. Repeating it is very natural.

A careful pronunciation would be:

dar ân forushgâh yek shalvâr-e tire va yek pirâhan-e roshan didam

A few pronunciation notes:

• در = dar
• آن = ân
• فروشگاه = forushgâh
• شلوار = shalvâr
• پیراهن = pirâhan
• دیدم = didam

In everyday speech, some sounds may become a little more relaxed, but this pronunciation is a good standard model.

It is neutral standard Persian and works well in both writing and careful speech.

In more colloquial speech, people might say something like:

تو اون فروشگاه یه شلوار تیره و یه پیراهن روشن دیدم

Differences:

• در becomes تو
• آن becomes اون
• یک becomes یه

But the original sentence is perfectly natural and correct in standard Persian.