فقدت محفظة أمس.

Because standard Arabic writing usually leaves out short vowels.

So فقدت could represent:

• فقدتُ = I lost
• فقدتْ = she lost

In fully vowelled text, the ending would make it clear. In normal everyday writing, you rely on context to know which one is meant.

In Arabic, the verb itself often contains the subject.

So instead of saying something like I lost, Arabic can simply use a verb form meaning lost-I. If the intended form here is فقدتُ, the ـتُ ending already tells you the subject is I.

That is very normal in Arabic. Subject pronouns are often omitted because the verb already shows who did the action.

It is the past-tense form of the verb فقد, which means to lose or sometimes to be missing / to miss depending on context.

In this sentence, it means lost in the sense of misplacing something.

So the core structure is:

• فقدت = lost / I lost / she lost

Because محفظة has no الـ at the beginning.

In Arabic:

• محفظة = a wallet
• المحفظة = the wallet

So the noun here is indefinite, which is why English translates it with a.

It is in the accusative case because it is the direct object of the verb فقدت.

The thing being lost is the object, so it takes the accusative ending in fully vocalized Arabic:

• محفظةً

In ordinary unvowelled writing, you usually just see محفظة.

Because short vowel endings are usually not written in everyday Arabic text.

So although the fully vocalized form would be محفظةً, normal writing usually leaves off the vowel marks and just writes:

• محفظة

Also, because the word ends in ة (taa marbuuTa), the tanween is placed on that final letter when vowels are shown.

Because verb-first word order is very common in Modern Standard Arabic.

This sentence is naturally structured as:

• فقدت = verb
• محفظة = object
• أمس = time expression

So the pattern is basically:

lost + a wallet + yesterday

That is a normal and natural Arabic sentence pattern.

أمس means yesterday and functions as an adverbial expression of time.

It tells you when the action happened.

So:

• فقدت محفظة أمس = I lost a wallet yesterday

There is no preposition needed before أمس.

Yes. Arabic word order is fairly flexible, especially with time expressions.

For example, these are also possible in principle:

• فقدت أمس محفظة
• أمس فقدت محفظة

But the original order, فقدت محفظة أمس, is straightforward and natural.

Changing the position usually affects emphasis more than basic meaning.

Yes. Because it ends in ة, it is grammatically feminine.

That does not mean the wallet itself is biologically female, of course. It just means that if you later describe it with an adjective or refer back to it with a pronoun, Arabic grammar will treat it as feminine.

For example, an adjective modifying محفظة would normally appear in the feminine form.

Yes, a little.

Without short vowels, فقدت could mean either:

• I lost
• she lost

So the written sentence by itself is ambiguous unless context makes the meaning clear.

This is very common in Arabic. Readers are expected to use context to resolve such ambiguities.