Seems like an interesting effort. A developer is building an alternative Java-based backend to Lemmy’s Rust-based one, with the goal of building in a handful of different features. The dev is looking at using this compatibility to migrate their instance over to the new platform, while allowing the community to use their apps of choice.
1-2 days is enough to learn the basics, but I doubt you’ll be as nearly as productive as with something you’ve been using for years. Keep in mind that new languages also mean new frameworks, etc, some which take years to actually master, but at least months to get a good handle on them.
Also, from my understanding, Rust is a bit of a paradigm shift.