من عادة صديقتي أن تمشي في هذا الشارع كل مساء.

It is an idiomatic way to say it is my friend’s habit to... or my friend usually...

Literally, من عادة صديقتي is something like among my friend’s habits or it is from my friend’s habit/custom. In natural English, we do not usually translate من word-for-word here. The whole expression works as a set phrase.

So:

• من عادة صديقتي أن تمشي...
  = It is my friend’s habit to walk...
• More naturally: My friend usually walks...

Here من is not being used in its basic literal sense of from. In this pattern, من عادة + noun + أن..., it helps form an idiomatic expression meaning it is someone’s habit to...

So although من often means from, here you should learn the whole chunk:

• من عادة فلان أن... = It is X’s habit to...

This is very common in Arabic. It is better to think of it as a fixed expression rather than translate each word separately.

Because Arabic commonly uses the indefinite noun in this expression:

• من عادة فلان أن...

Using عادة without الـ gives the sense of a habit / part of the habit-pattern of...

If you said من العادة, that would usually sound more like it is customary or it is the custom, often in a more general sense, not specifically someone’s personal habit in the same way.

So:

• من عادة صديقتي... = it is my friend’s habit...
• من العادة أن... = it is customary to...

This is an iḍāfa construction, often called a genitive construction.

• عادة = habit
• صديقتي = my female friend

Together:

• عادة صديقتي = my friend’s habit

In an iḍāfa:

1. the first noun is the thing possessed: عادة
2. the second noun shows who it belongs to: صديقتي

So Arabic says habit of my friend, where English says my friend’s habit.

Also, صديقتي contains the suffix ـي, meaning my.

Yes, صديقتي literally means my female friend:

• صديقة = female friend
• صديقتي = my female friend

In some contexts, it can also mean my girlfriend, but in Modern Standard Arabic the basic meaning is simply my female friend. Context determines whether a romantic meaning is intended.

Since the rest of the sentence is neutral, the default reading is just my female friend.

أن introduces a verb clause that works a bit like an infinitive in English.

So:

• أن تمشي = to walk

That is why the sentence can be understood as:

• It is my friend’s habit to walk in this street every evening.

Arabic often uses أن + imperfect verb where English uses to + verb.

Examples:

• أريد أن أذهب = I want to go
• من عادته أن يقرأ = It is his habit to read

Because its subject is صديقتي, which is feminine singular.

The verb تمشي means she walks or she may walk / to walk depending on context. Here, after أن, it means to walk with an implied feminine subject:

• أن تمشي = that she walk / to walk

Arabic verbs show gender and number, so the form matches صديقتي.

If the subject were masculine, you would get:

• من عادة صديقي أن يمشي...
  = It is my male friend’s habit to walk...

Arabic usually does not need a separate subject pronoun when the verb already shows the subject.

Here, تمشي already tells you the subject is:

• third person
• singular
• feminine

So تمشي already contains the idea of she walks.

A separate pronoun like هي is unnecessary here unless you want extra emphasis.

Yes. After أن, the imperfect verb is normally in the subjunctive.

With a fully vocalized form, this would be:

• تَمْشِيَ

But in normal Arabic writing, short vowels are usually not written, so it appears simply as:

• تمشي

That is why the spelling looks unchanged even though the grammatical mood has changed.

This is especially common with verbs ending in a weak letter, like مشى / يمشي.

Yes, English usually says on this street, but Arabic often uses في in places where English uses in or on.

So:

• في هذا الشارع literally = in this street
• natural English = on this street

This is just a normal difference between the two languages. When talking about location in a street, في الشارع is very common Arabic usage.

هذا means this, so:

• هذا الشارع = this street

The noun after هذا usually takes الـ:

• هذا الكتاب = this book
• هذه المدينة = this city
• هذا الشارع = this street

So Arabic says literally this the-street, but in English we simply say this street.

كل مساء means every evening.

• كل = every / all
• مساء = evening

Arabic often uses time expressions directly, without a preposition like in or on:

• كل يوم = every day
• كل صباح = every morning
• كل مساء = every evening

So the sentence naturally ends with كل مساء to show repeated time.

Grammatically, this kind of expression functions adverbially: it tells when the action happens.

The sentence is built around an idiomatic nominal structure:

• من عادة صديقتي = it is my friend’s habit
• أن تمشي في هذا الشارع كل مساء = to walk on this street every evening

So the whole sentence means:

• It is my friend’s habit to walk on this street every evening.

A very literal structural interpretation would be something like:

• Among my friend’s habits is walking on this street every evening.

That sounds unnatural in English, but it helps show how the Arabic is put together.

Yes. Arabic also allows more direct alternatives, for example:

• صديقتي تمشي في هذا الشارع كل مساء.
  = My friend walks on this street every evening.

or

• اعتادت صديقتي أن تمشي في هذا الشارع كل مساء.
  = My friend is used to walking on this street every evening / My friend habitually walks on this street every evening.

The original version with من عادة صديقتي أن... is slightly more formal and explicitly emphasizes habit.