Books written in a constructed language?

Inspired by this query on r/WeirdLit, I'm interested in books that are written in an invented language. To be more specific, I'm looking for books that:

• Are mainly or entirely written in a made-up language (as opposed to works which just feature a conlang);
• Preferably written in a language invented by the author themselves (as opposed to an existing conlang like Esperanto);
• Are not necessarily meaningful or interpretable (so the Codex Seraphinianus would qualify as well as something like Riddley Walker).