وقتی خواهرم لبخند میزند، همه خوشحال میشوند.

In Farsi, possession is often shown by attaching a short ending to the noun.

• خواهر = sister
• -م = my

So:

• خواهرم = my sister

This ending is called an enclitic pronoun. You will see the same pattern with many nouns:

• دوستم = my friend
• کتابم = my book
• مادرم = my mother

So instead of using a separate word for my, Farsi often just adds -م to the end.

وقتی means when in this sentence.

So:

• وقتی خواهرم لبخند میزند = when my sister smiles

It introduces a time clause, just like English when.

A few related words:

• وقتی = when
• هر وقت = whenever
• وقتی که = when / at the time that

In everyday speech, وقتی by itself is very common.

Farsi usually prefers subject–object–verb order, and the verb often comes at the end of the clause.

In this sentence:

• وقتی خواهرم لبخند میزند literally: when my sister smile does
• همه خوشحال میشوند literally: everyone happy become

That is normal Farsi structure.

A native English speaker often expects the verb earlier, but in Farsi it is very common to wait until the end to get the main action.

In Farsi, many actions are expressed with a noun + light verb combination.

Here:

• لبخند = smile
• زدن = to hit / strike, but in combinations it can help form other meanings
• لبخند زدن = to smile

So لبخند میزند literally looks like she/he strikes a smile, but it simply means she/he smiles.

This kind of structure is extremely common in Farsi. For example:

• تلفن زدن = to call / to telephone
• حرف زدن = to talk
• تصمیم گرفتن = to decide

So this is a normal pattern to learn, not something strange or poetic.

Yes — in standard spelling, these are usually written with a half-space:

• می‌زند
• می‌شوند

The little element می marks the present/imperfective form.

So the more standard written version of the whole sentence is:

وقتی خواهرم لبخند می‌زند، همه خوشحال می‌شوند.

Many people omit the half-space when typing informally, so میزند and میشوند are very common online. But if you want careful standard writing, use:

• می‌زند
• می‌شوند

می is a marker often used for the present habitual, general present, or ongoing/imperfective sense.

Here:

• می‌زند = smiles / is smiling / does smile, depending on context
• می‌شوند = become / get / are becoming

In a sentence like this, English usually translates it as a simple present:

• When my sister smiles, everyone becomes happy
• more naturally: When my sister smiles, everyone gets happy

So می is helping form the normal present-tense pattern.

Because the verb ending already tells you the subject person/number.

می‌زند is third person singular, so it means:

• he/she/it smiles

Since خواهرم is already stated, there is no need to add او (she/he).

This is very normal in Farsi. Subject pronouns are often omitted when the meaning is clear.

For example:

• خواهرم می‌آید = my sister comes / is coming
• literally no separate she is needed

همه means everyone / all. Even though English everyone is grammatically singular, in Farsi همه often goes with a plural verb, especially when referring to people as a group.

So:

• همه خوشحال می‌شوند = everyone becomes happy / everyone gets happy

That plural -ند ending in می‌شوند matches the idea of multiple people.

This is a very common and natural pattern in Farsi.

Literally, it means become happy.

Breakdown:

• خوشحال = happy
• شدن = to become
• می‌شوند = they become / they get

So:

• همه خوشحال می‌شوند = everyone becomes happy / everyone gets happy

In natural English, you might also say:

• everyone is happy
• everyone gets happy
• everyone becomes happy

Depending on context, all can work, but the literal Farsi structure is closer to become happy.

A natural pronunciation is roughly:

vaqti khâharam labkhand mizane, hame khoshhâl mishan

A bit more carefully in standard pronunciation:

vaqti khâharam labkhand mizanad, hame khoshhâl mishavand

A few notes:

• خواهرم sounds like khâharam
• لبخند is pronounced labkhand
• In everyday speech, می‌زند often sounds like mizane
• می‌شوند in speech often becomes mishan

So written and spoken forms can differ somewhat.

It is a mix of standard written structure and common everyday meaning.

The written verb forms:

• می‌زند
• می‌شوند

are standard and appropriate for writing.

In everyday spoken Farsi, people often say something closer to:

وقتی خواهرم لبخند می‌زنه، همه خوشحال می‌شن.

That spoken version is more conversational.

So the sentence you were given is a good standard form to learn, even if casual speech sounds a little different.

The comma separates the when-clause from the main clause:

• وقتی خواهرم لبخند می‌زند،
• همه خوشحال می‌شوند.

This works a lot like English:

• When my sister smiles, everyone gets happy.

In Persian punctuation, commas are commonly used this way to make the sentence easier to read.

Yes. Farsi also has the verb لبخند زدن as the normal expression for to smile, but you may also encounter:

• لبخند زدن = to smile
• خندیدن = to laugh
• تبسم کردن = to smile (more literary or formal in some contexts)

For this sentence, لبخند می‌زند is very natural and common. It specifically means smiles, not laughs.