När jag mötte hennes syster i går, märkte jag att hon var mycket gladare än förra veckan.

Because Swedish follows the V2 rule in main clauses: the finite verb must come in the second position.

Here, the sentence starts with the subordinate clause:

När jag mötte hennes syster i går

After that, the main clause begins, and in a Swedish main clause the verb comes second:

• När jag mötte hennes syster i går, märkte jag ...
• literally: When I met her sister yesterday, noticed I ...

So the inversion is normal and required here.

Compare:

• Jag märkte att hon var gladare.
• I går märkte jag att hon var gladare.
• När jag mötte hennes syster i går, märkte jag att hon var gladare.

In all of these, the verb of the main clause stays in second position.

Att means that and introduces a subordinate clause.

So:

• märkte jag att hon var mycket gladare
• I noticed that she was much happier

In English, that is often optional:

• I noticed (that) she was happier

In Swedish, att is very commonly kept and sounds natural here.

Because the sentence is talking about a situation in the past.

The main verb is also in the past:

• mötte = met
• märkte = noticed
• so var = was

This keeps the whole sentence in a consistent past-time frame:

• När jag mötte ... märkte jag att hon var ...

Using är would usually suggest present time, which would not fit as naturally with the rest of this sentence.

Grammatically, hon means she, but the sentence itself is a little ambiguous.

It could refer to:

• hennes syster = her sister

But without more context, a learner might wonder whether it could refer to another previously mentioned female person.

In normal reading, the most likely interpretation is that hon refers to her sister, because that is the most recent female person mentioned.

So the most natural reading is:

• When I met her sister yesterday, I noticed that she (the sister) was much happier than last week.

This is a very common Swedish question.

Swedish uses:

• sin / sitt / sina for a reflexive possessor, when the possessor is the subject of the same clause
• hennes / hans / deras when it is not reflexive

In this sentence:

• jag is the subject of the clause
• hennes syster belongs to some other woman, not to jag

So hennes is correct.

Compare:

• Hon träffade sin syster. = She met her own sister.
• Jag träffade hennes syster. = I met her sister.

So sin would be wrong here because the subject is jag, not the woman whose sister it is.

Mötte is the past tense of möta, which usually means met or encountered.

It often suggests physically coming across someone or meeting them.

So:

• Jag mötte henne på gatan. = I met / ran into her on the street.

A learner may compare it with träffade:

• träffade can also mean met
• in many situations, träffade sounds a bit broader and more common in everyday speech

In this sentence, mötte hennes syster is perfectly natural and means that the speaker encountered or met the sister yesterday.

In standard Swedish, i går is normally written as two words and means yesterday.

Literally, it comes from an older expression meaning something like on/at yesterday’s day, but for learners it is best just to learn it as a fixed expression:

• i dag = today
• i morgon = tomorrow
• i går = yesterday

So in the sentence:

• i går = yesterday

In Swedish, many time expressions do not need a preposition.

So Swedish says:

• förra veckan = last week
• förra året = last year
• nästa månad = next month

This is similar to English, where you also say last week, not in last week.

So:

• gladare än förra veckan = happier than last week

Gladare is the comparative form of glad:

• glad = happy
• gladare = happier
• gladast = happiest

Many short Swedish adjectives form the comparative by adding -are and the superlative by adding -ast.

Examples:

• snäll → snällare → snällast
• rik → rikare → rikast

So:

• mycket gladare = much happier

Because glad normally takes the regular comparative ending -are.

So the normal form is:

• gladare = happier

And mycket gladare means:

• much happier

Swedish does use mer for many longer adjectives, for example:

• intressant → mer intressant

But with glad, the ordinary comparative is gladare, not mer glad.

Än means than in comparisons.

So:

• gladare än förra veckan
• happier than last week

It is the standard word used after comparatives in Swedish:

• större än = bigger than
• snabbare än = faster than
• bättre än = better than

The comma separates the introductory subordinate clause from the main clause:

• När jag mötte hennes syster i går, märkte jag ...

This makes the sentence easier to read.

In Swedish, comma use is often a bit less rigid than in English, and you may sometimes see similar sentences without a comma. But with a longer introductory clause like this one, the comma is very natural and helpful.

It is a subordinate time clause introduced by när = when.

It tells us when the action in the main clause happened.

Structure:

• När ... = when ...
• märkte jag ... = I noticed ...

So the sentence means:

• When I met her sister yesterday, I noticed ...

This kind of när clause is very common in Swedish.

Because this is a subordinate clause, and Swedish word order changes in subordinate clauses.

In the main clause, Swedish uses the V2 rule:

• märkte jag

But in the subordinate clause after att, the subject usually comes before the verb in the normal way:

• att hon var mycket gladare

So:

• main clause: märkte jag
• subordinate clause: hon var

That contrast is completely normal in Swedish.

Yes. In this sentence, mycket gladare means much happier.

Word for word:

• mycket = much
• gladare = happier

So it works very neatly.

A learner should note that mycket can modify a comparative adjective this way:

• mycket bättre = much better
• mycket större = much bigger
• mycket gladare = much happier

In this sentence, när is most naturally understood as when, referring to one specific event in the past:

• När jag mötte hennes syster i går ...
• When I met her sister yesterday ...

Because i går gives a specific time, it clearly points to a single occasion, not a repeated one.

So here när means when, not whenever.