I love this!
I've run into a bug though: after completing the first section in "sitelen pona". clicking on Start in the Review block makes it show an empty window with no buttons. I can see a javascript error in the console: "Uncaught ReferenceError: char is not defined" in main.js. Tried clearing all site data & cookies, same result.
I'd really like to complete all the sections, so it would be awesome if this could perhaps be patched. Thanks!
Edit: Bug has been fixed :)