Learn Swedish: Publiken är förväntansfulla när de tittar på livesändningen. - The audience is expectant when they watch the live broadcast.

This is the core of semantic agreement. Even though publiken is grammatically singular, it refers to a collective group of people. In Swedish, you often use the plural adjective form (förväntansfulla) when you are thinking about the individual people making up that group rather than the group as a single unit.

Why does the sentence use the pronoun de instead of den to refer back to publiken?

This follows the exact same logic as the adjective. Because the sentence treats the collective noun publiken as a group of individuals, it uses the plural pronoun de (they) instead of the singular den (it). If you switch to the plural perspective for the adjective, you must keep it for the pronouns as well.

Is it also correct to use singular agreement for everything here?

Yes, you could write publiken är förväntansfull när den tittar, which uses strict grammatical agreement. However, semantic agreement is often preferred and sounds much more natural in modern Swedish when a group of people is doing something active or feeling a human emotion.

How does the word livesändningen work? Is it partly English?