Can you simply ask them to walk through their submission line by line with you, explaining what it's doing?
This. Code reviews, especially with junior devs, should always be done as a conversation. It's an opportunity to learn (from both sides), not just a a bunch of "bad implementation. rewrite" thrown in the PR.
~~Makes sense, I think most users I've seen are french speakers. Which org? ~~
Edit: nvm I found them, it's Les Soulèvements de la Terre. Thank you!