Když stojím před zrcadlem, vidím, že jsem ještě unavený.

Když means when in the sense of introducing a time clause.

So Když stojím před zrcadlem... = When I stand in front of the mirror...

A learner may confuse když with words like:

• až = when / once for a future point
• jestli / pokud = if

Here, když is correct because it introduces a situation happening at the same time as the main clause.

Stojit is not the infinitive. The infinitive is stát = to stand.

Stojím is the 1st person singular present tense form: I stand / I am standing.

Conjugation of stát in this meaning:

• stojím = I stand
• stojíš = you stand
• stojí = he/she/it stands
• stojíme = we stand
• stojíte = you plural/formal stand
• stojí = they stand

So Když stojím... literally means When I am standing...

After the preposition před when it means in front of, Czech uses the instrumental case.

• dictionary form: zrcadlo = mirror
• instrumental singular: zrcadlem

So:

• před zrcadlem = in front of the mirror

This is a very common pattern:

• před domem = in front of the house
• před školou = in front of the school
• před autem = in front of the car

So the case change is required by the preposition.

Czech punctuation usually separates subordinate clauses with commas more consistently than English does.

This sentence has three parts:

1. Když stojím před zrcadlem
2. vidím
3. že jsem ještě unavený

So the commas mark clause boundaries:

• Když stojím před zrcadlem, vidím, že jsem ještě unavený.

The first comma closes the when-clause.
The second comma introduces the that-clause after vidím.

In Czech, this punctuation is standard and important.

Že means that and introduces a content clause.

So:

• vidím = I see
• že jsem ještě unavený = that I am still tired

Together:

• vidím, že jsem ještě unavený = I see that I am still tired

In Czech, že is very commonly used after verbs of saying, thinking, knowing, noticing, and seeing:

• vím, že... = I know that...
• myslím, že... = I think that...
• říká, že... = he/she says that...

Jsem is the 1st person singular of být = to be.

So:

• jsem unavený = I am tired

The clause že jsem ještě unavený literally means:

• that I am still tired

This is normal Czech word order after že.

Yes. Unavený is the masculine singular form of the adjective unavený = tired.

That means the sentence, as written, sounds like it is spoken by a male speaker.

If the speaker were female, it would be:

• Když stojím před zrcadlem, vidím, že jsem ještě unavená.

So the adjective agrees with the person speaking.

This is something English does not show, but Czech often does.

Here ještě means still.

So:

• jsem ještě unavený = I am still tired

Depending on context, ještě can also mean things like:

• yet
• more
• another

But in this sentence, still is the natural meaning.

Examples:

• Ještě spí. = He/She is still sleeping.
• Ještě nevím. = I still don’t know / I don’t know yet.
• Ještě kávu? = More coffee?

Both are understandable, but že jsem ještě unavený is the more neutral and natural order.

In Czech, short forms like jsem often tend to appear early in the clause, usually in the second position area. This is part of a broader Czech word-order pattern involving clitics.

So:

• natural: že jsem ještě unavený
• less neutral: že ještě jsem unavený

A beginner does not need to master all clitic rules immediately, but it is useful to notice that forms like jsem, jsem, se, si, ho, mu often appear near the beginning of the clause.

It can mean both.

Czech present tense often covers what English expresses with either:

• the simple present: I stand
• the present continuous: I am standing

So Když stojím před zrcadlem... can correspond to:

• When I stand in front of the mirror...
• When I’m standing in front of the mirror...

The exact English translation depends on context, but the Czech form stays the same.

Yes, but it would not mean exactly the same thing.

• Když stojím před zrcadlem = When I stand / am standing in front of the mirror
• Když jsem před zrcadlem = When I am in front of the mirror

The second version is more general. It only says where you are.
The original sentence specifically says you are standing there.

So the original is more vivid and precise.

It is literally I see, but in sentences like this it often also has the sense of I can tell or I realize from what I see.

So:

• vidím, že jsem ještě unavený

can feel like:

• I see that I’m still tired
• I can tell that I’m still tired

The mirror context makes that especially natural: you look at yourself and notice that you still look tired.

Only the final adjective would need to change:

• masculine speaker: Když stojím před zrcadlem, vidím, že jsem ještě unavený.
• feminine speaker: Když stojím před zrcadlem, vidím, že jsem ještě unavená.

Everything else stays the same.

That is because the adjective agrees with the gender of the subject I, even though Czech does not usually state the pronoun já here.