The quizzes are because I feel like I need to do something with the translations, other than just karaoke.

The translations are because translations are generally a good way to develop a conlang. Songs specifically tend to be bite-sized projects, so it's harder to feel overwhelmed by them compared to a project like translating the Bible or every episode of MLP:FiM or something like that; and the constraints of rhyme and meter etc that come with most songs help guide most obviously the forms of new words, but also things like grammar or phrasing or the semantics of pre-existing words.

The conlang is... I dunno, there are a few reasons for it, I guess. Experimenting with new sounds and forms of grammar in a conlang, where there's no-one really judging your grammar, and no obvious right and wrong, can be a good way to get used to features in a foreign language before you study it, in a zero-stress environment. Conlangs can also be a good way to apply linguistic theories in practice, and they can also serve as secret codes or just a general form of audiovisual self-expression. But for me, I think the main appeal of my conlangs are that they express the history and culture of this fictional world. That if you spend a long enough time conlanging that you've got like slang and idioms, different dialects and registers, loanwords from other fictional languages, dated or obsolete words or archaisms and fossils, words for unique cultural concepts, vulgarities and tag questions and filler words and interjections, an image of how things are naturally phrased, an image of the language's past and future and relatives... The language starts to feel like a portal to the other world.

Which I guess still leaves the question of why I want to invent this other world. And I dunno, one part's probably escapism, yeah, but generally I think I can explore and comment on myself and the world around me by exploring this fictional world and the lives of its inhabitants.