من منتظر خواهرم خواهم بود، اما او قرار را فراموش نخواهد کرد.

Because this sentence uses the future tense, which in standard Persian is often made with:

• a form of خواستن used as an auxiliary: خواهم / خواهی / خواهد / ...
• plus the past stem of the main verb

So:

• خواهم بود = I will be
• نخواهد کرد = he/she will not do

In this sentence:

• منتظر ... خواهم بود literally means I will be waiting / I will be in a waiting state
• فراموش نخواهد کرد literally means he/she will not forget

So the future is built analytically, not with a single word.

منتظر is basically an adjective/state word meaning waiting or expectant. Persian often says to be waiting rather than using a single simple verb equivalent to English wait.

So:

• منتظر بودن = to be waiting
• من منتظر خواهرم خواهم بود = I will be waiting for my sister

This is very natural Persian.

Because Persian handles this differently from English. With منتظر بودن, the person or thing being awaited usually comes after منتظر with ezafe:

• منتظرِ خواهرم
• literally: waiting-of my sister
• naturally: waiting for my sister

In normal Persian spelling, the ezafe is usually not written, so you see:

• منتظر خواهرم

But it is understood as:

• منتظرِ خواهرم

So the idea of English for is built into the Persian structure, not expressed by a separate preposition.

خواهرم means my sister.

It is made of:

• خواهر = sister
• ـم = my

So Persian often attaches possessive endings directly to nouns:

• خواهرم = my sister
• خواهرت = your sister
• خواهرش = his/her sister

This is very common and important in Persian.

Yes, very often it can.

Since خواهم بود already shows first person singular (I will be), Persian does not always need the pronoun من.

So both are possible:

• من منتظر خواهرم خواهم بود
• منتظر خواهرم خواهم بود

Including من can add clarity, contrast, or emphasis. In a sentence with two different people like this one, keeping من can be especially helpful.

Yes, Persian often drops subject pronouns when the verb already makes the subject clear.

So you could say:

• ... اما قرار را فراموش نخواهد کرد.

However, او is included here to make the contrast clearer:

• I will be waiting, but she/he will not forget the appointment.

So او adds explicit contrast and helps the sentence sound clearer.

Here, قرار means something like:

• appointment
• meeting
• date
• arrangement

The exact translation depends on context. In this sentence, it most likely means the appointment/meeting/date.

So:

• قرار را فراموش نخواهد کرد = he/she will not forget the appointment/date

را marks a specific direct object.

So:

• قرار را = the appointment/date as a definite, specific thing

In this sentence, it is not just any appointment in general; it is a particular one already known from context.

That is why را is used.

Very roughly:

• قرار = an appointment / appointment in general
• قرار را = the appointment / that appointment

In the Persian future tense, the negative normally goes on the auxiliary:

• خواهد کرد = will do
• نخواهد کرد = will not do

So the نـ attaches to خواهد, not to کرد.

That is the normal pattern for negating this kind of future construction.

Because فراموش کردن is a very common Persian compound verb.

It is made of:

• فراموش = forgetfulness / forgotten
• کردن = to do

Together:

• فراموش کردن = to forget

Persian uses many compound verbs like this. So instead of a single simple verb, it often uses:

• a noun/adjective-like element
• plus a light verb such as کردن, شدن, دادن, etc.

This is one of the most important patterns in Persian vocabulary.

Yes, usually.

In everyday spoken Persian, speakers often use the present tense to talk about the future when the context is clear:

• فراموش نمی‌کند can mean he/she won't forget

But the sentence you have uses the more explicit future tense:

• فراموش نخواهد کرد = he/she will not forget

This is standard and clear, and can sound a bit more formal, written, or deliberate than everyday speech.

The same idea applies to:

• منتظر خواهرم خواهم بود
  versus a more conversational future-like present form in some contexts.

Persian typically puts the main verb at the end of the clause.

So the structure is roughly:

• subject + complement/object + verb

Here:

• من = subject
• منتظر خواهرم = complement
• خواهم بود = verb

So:

• من منتظر خواهرم خواهم بود

This end-of-clause verb position is one of the biggest word-order differences from English.

اما means but.

It connects the two clauses and shows contrast:

• I will be waiting for my sister, but she will not forget the appointment.

It is a very common conjunction in Persian, especially in writing and careful speech.

A helpful transliteration is:

• man montazere khâharam khâham bud, ammâ u gharâr râ farâmush nakhâhad kard

A few notes:

• منتظرِ is pronounced with an e sound before the next word: montazere
• خواهم is roughly khâham
• نخواهد is roughly nakhâhad
• را in careful speech is râ, though in colloquial speech it often sounds more like ro

Yes, it is grammatically correct and understandable.

That said, in everyday spoken Persian, people often prefer less explicit future marking. For example, depending on context, a more conversational style might avoid خواهم بود / نخواهد کرد and use present forms instead.

But as a learning sentence, this is very useful because it clearly shows:

• the future tense
• possession with ـم
• object marking with را
• a negative future form
• normal Persian word order