"Han försökte lära sig läxan."

Translation: He tried to learn the lesson.

[Plugghest]

Are lektion and läxa interchangeable, or does läxa refer to lessons learned during homework?

[Zmrzlina]

No. While homework is uncountable in English, läxa is countable as one of the tasks assigned for homework. The translations here are idiomatic, meaning being forced to learn or adapt.

[Arnauti]

Also, the 1 hr session you might have with a teacher and other students can only be called en lektion, never 'en läxa'. Also a chapter in a book can be Lektion 1, 'Lesson 1', but it'll never have the title "Läxa 1" (that would be 'Homework 1')

[Sjodni]

And on Duolingo, he succeeded!

[ParisAndEmilia]

Basically this lesson/läxa is if he had done something bad and had to learn a lesson