من درباره این تصمیم با خواهرم صحبت کردم.

Yes, من can be omitted.

Persian verbs usually show the subject, so کردم already tells you the subject is I. That means:

• من درباره این تصمیم با خواهرم صحبت کردم.
• درباره این تصمیم با خواهرم صحبت کردم.

Both can mean I talked with my sister about this decision.

Including من adds emphasis or clarity, especially if you want to contrast I with someone else.

Because standard Persian word order is usually Subject + other elements + Verb.

So in this sentence:

• من = I
• درباره این تصمیم = about this decision
• با خواهرم = with my sister
• صحبت کردم = talked

The verb normally comes last in Persian, much more often than in English.

درباره means about / concerning / regarding.

In this sentence, درباره این تصمیم means about this decision.

A very common synonym is راجع به, so you could also hear:

• راجع به این تصمیم با خواهرم صحبت کردم.

That has basically the same meaning.

Yes, there is an ezafe sound there in pronunciation.

It is pronounced:

• دربارهٔ این
• darbâre-ye in

In everyday writing, the ezafe is often not written, so you may just see:

• درباره این

But when reading carefully, you should understand it as darbâre-ye in.

• این = this
• تصمیم = decision

So این تصمیم means this decision.

Unlike English, Persian does not use a/an/the, so تصمیم can mean decision / the decision / a decision depending on context.

با means with.

خواهرم breaks down like this:

• خواهر = sister
• -م = my

So خواهرم means my sister.

Therefore:

• با خواهرم = with my sister

That -م ending is a very common possessive ending in Persian.

Because Persian often uses compound verbs.

Here:

• صحبت = conversation / speaking
• کردم = I did

Together, صحبت کردم means I talked / I spoke.

This is very common in Persian. Instead of a single verb, Persian often uses a noun or verbal element plus کردن.

A natural pronunciation is:

man darbâre-ye in tasmim bâ khâharam sohbat kardam

A few notes:

• درباره → darbâre
• تصمیم → tasmim
• خواهرم → khâharam
• صحبت → sohbat
• کردم → kardam

The kh in khâharam is like the ch in German Bach or Scottish loch.

It can mean both, depending on context.

• صحبت کردم can be understood as I talked
• It can also be I spoke

In this sentence, because of با خواهرم (with my sister), talked with my sister is the most natural English translation.

Yes, often you can.

For example:

• درباره این تصمیم با خواهرم حرف زدم.

This also means I talked with my sister about this decision.

The difference is mostly one of style:

• صحبت کردم sounds a bit more neutral or formal
• حرف زدم is often a bit more conversational

Both are very common.

کردم is simple past.

It comes from کردن = to do, and here it is part of the compound verb صحبت کردن = to talk / to speak.

So:

• صحبت کردم = I talked / I spoke

The -م on کردم marks I.

Because there is no direct object here.

را marks a definite direct object, but in this sentence:

• درباره این تصمیم is a prepositional phrase: about this decision
• با خواهرم is another prepositional phrase: with my sister

So there is nothing here that needs را.

Yes, it is completely natural and standard.

It sounds like normal, everyday Persian. A native speaker would understand it immediately.

You might also hear small variations such as:

• با خواهرم درباره این تصمیم صحبت کردم.
• راجع به این تصمیم با خواهرم صحبت کردم.

These are also natural.

Yes, it can.

For example, these are both natural:

• من درباره این تصمیم با خواهرم صحبت کردم.
• من با خواهرم درباره این تصمیم صحبت کردم.

Both mean the same thing.

The second version may feel slightly more natural to some speakers, but both are correct. Persian allows some flexibility in the order of these phrases, as long as the verb usually stays at the end.