Jag förväntar mig inte ett snabbt svar i kväll, eftersom hon jobbar sent.

Because the Swedish verb is förvänta sig, which is a reflexive verb. That means it normally goes together with a reflexive pronoun:

• jag förväntar mig = I expect
• du förväntar dig = you expect
• han/hon förväntar sig = he/she expects

So mig is not optional here. In this sentence, förväntar mig works as the verb phrase expect.

In a normal Swedish main clause, the finite verb usually comes early, and sentence adverbs like inte usually come after the finite verb.

So the pattern is:

• Jag förväntar mig inte ...

not

• Jag inte förväntar mig ...

A helpful way to see it:

• Jag = subject
• förväntar = finite verb
• mig = reflexive pronoun
• inte = not

Swedish word order is often stricter than English here.

Because svar is an ett-word in Swedish:

• ett svar = an answer

Adjectives must agree with the noun, so with an ett-word, the adjective usually takes -t in the singular indefinite form:

• en snabb bil = a fast car
• ett snabbt svar = a quick answer

So both the article and the adjective have to match svar.

It changes because it describes an ett-word noun: svar.

Basic pattern:

• en snabb fråga = a quick question
• ett snabbt svar = a quick answer

So snabbt is just the form of snabb used with an ett-word in the singular indefinite form.

I kväll means this evening / tonight.

Swedish often uses the present tense for future meaning when the time is clear from context. Since i kväll already tells you the time, Swedish does not need a separate future form here.

So:

• Jag förväntar mig inte ett snabbt svar i kväll
  = I don’t expect a quick answer tonight

This is very natural Swedish.

Yes. Both i kväll and ikväll are used.

In modern Swedish, ikväll as one word is very common, especially in everyday writing.
So these are both acceptable:

• i kväll
• ikväll

The meaning is the same.

Yes. Eftersom means because / since, and it introduces a subordinate clause.

The clause is:

• eftersom hon jobbar sent

Here the word order is normal for a subordinate clause. In this particular example, there is no big visible difference from English, but subordinate clauses matter in Swedish because sentence adverbs like inte usually come before the verb there.

For example:

• ... eftersom hon inte jobbar sent
  = ... because she is not working late

Notice how inte comes before jobbar in the subordinate clause.

That is an important Swedish pattern.

Here sent means late.

The base adjective is sen = late, but when it is used in certain adverb-like ways, Swedish often uses the -t form:

• Hon kommer sent = She arrives late
• Han jobbar sent = He works late

So in this sentence, sent describes how late she is working.

Yes, arbetar would also be possible.

• jobbar = works, more everyday and conversational
• arbetar = works, a bit more formal or neutral

So:

• eftersom hon jobbar sent sounds very natural in everyday Swedish
• eftersom hon arbetar sent is also correct, but slightly less casual

No. They are different.

• förvänta sig = to expect
• vänta på = to wait for

So:

• Jag förväntar mig ett svar = I expect an answer
• Jag väntar på ett svar = I am waiting for an answer

This is a very common distinction for learners, because English expect and wait for are quite different, and Swedish keeps them clearly separate too.

Yes, absolutely. Swedish often moves time expressions to the front.

For example:

• I kväll förväntar jag mig inte ett snabbt svar, eftersom hon jobbar sent.

Notice what happens: when I kväll comes first, the finite verb förväntar must still stay in the second position. So jag moves after the verb:

• I kväll förväntar jag mig inte ...

This is a very important Swedish word-order rule, often called V2 word order.

In careful speech, jag is often pronounced something like yah. In everyday spoken Swedish, it is very often reduced, and many speakers say something closer to ja.

So although it is spelled jag, you may hear:

• jag sounding like yah
• or more casually like ya

That is completely normal in spoken Swedish.