انا لسه مستني تحويل من صاحبتي على حساب التوفير.

Because Egyptian Arabic normally does not use a present-tense form of to be.

So أنا مستني literally looks like I waiting, but it naturally means I am waiting or I’m in a waiting state.

That is very normal in Arabic:

• أنا تعبان = I’m tired
• هو موجود = he’s here / he is present
• أنا مستني = I’m waiting

Here لسه means still.

So:

• أنا مستني = I’m waiting
• أنا لسه مستني = I’m still waiting

In other contexts, لسه can also relate to yet, especially with negatives:

• لسه ما وصلش = he hasn’t arrived yet

مستني is the active participle of استنى and is very commonly used in Egyptian Arabic to describe a current state.

So أنا لسه مستني sounds like:

• I’m still waiting
• I’m still in a waiting state

You could also say أنا لسه بستنى. That is also natural, but مستني is especially common and idiomatic here.

Because مستني is the form a male speaker would use.

If the speaker is female, it becomes:

• أنا لسه مستنية تحويل من صاحبتي على حساب التوفير

So the ending changes with the speaker’s gender.

Here تحويل means a transfer, especially a financial transfer or bank transfer.

In other contexts, تحويل can also mean other kinds of transfer or conversion, but in this sentence the banking meaning is the natural one.

It can mean either one.

صاحبتي literally refers to a female person connected to the speaker, but the exact meaning depends on context:

• my female friend
• my girlfriend

Arabic often leaves that to context, while English usually forces you to choose.

Because من marks the source.

So:

• تحويل من صاحبتي = a transfer from my female friend

That is exactly the same idea as English from.

In Egyptian Arabic, على الحساب is a very common way to talk about money going to / into an account.

So:

• على حساب التوفير means something like to the savings account or into the savings account

Even though على often literally means on, in banking language this phrasing is very natural.

People would understand it, but على حساب التوفير sounds more natural in everyday Egyptian Arabic for this kind of banking situation.

So:

• على حساب التوفير = more colloquial and natural here
• إلى حساب التوفير = understandable, but less idiomatic in this exact context

It is not stated directly in the sentence.

Arabic often leaves possession implied if the context already makes it clear whose account is meant. So على حساب التوفير can naturally be understood as referring to the relevant savings account in the conversation.

If you want to be explicit, you could say:

• على حساب التوفير بتاعي for a male speaker
• على حساب التوفير بتاعي is also commonly written this way informally
• على حساب التوفير بتاعتي for a female speaker talking about her own account

Because حساب التوفير is a noun phrase built like account of saving / savings account, and this is a normal Arabic way to form such expressions.

You do not have to translate the ال word-for-word every time. The whole phrase simply works as the standard expression for savings account.

So it is better to learn حساب التوفير as one banking phrase, not as separate pieces you must translate literally.

The sentence is built like this:

• انا = I
• لسه = still
• مستني = waiting
• تحويل = a transfer
• من صاحبتي = from my female friend / girlfriend
• على حساب التوفير = to/into the savings account

So the overall order is:

subject + still + state/action + thing awaited + source + destination

That order is very natural in Egyptian Arabic.

Yes, it is clearly colloquial, and it fits Egyptian Arabic very well.

Especially:

• لسه
• مستني

make it sound conversational rather than formal written Arabic.

A more formal Standard Arabic version would be quite different in style.