There's a C/C++ port which my team works on! As well as another member of the project to port it wrote a Golang BitTorrent client that uses it:
i2pd (I2P Daemon) это полнофункциональная реализация I2P клиента на языке C++.
I2P (Невидимый Интернет Протокол) это универсальный анонимный сетевой уровень. Все соединения через I2P анонимны и используют сквозное (end-to-end) шифрование, участники не раскрывают свои настоящие IP адреса.
I2P клиент это программа для построения и использования анонимных I2P сетей. Подобные сети обычно используются для анонимных peer-to-peer приложений (файлообмен, криптовалюты) и для анонимных клиент-серверных приложений (вебсайты, мессенджеры, чат-серверы).
I2P позволяет людям со всего мира общаться и делиться информацией без ограничений.
https://i2pd.website/
https://i2pd.readthedocs.io/ru/latest/index.html
I2P is pretty good, but I wouldn't rate the speed as acceptable. This is coming from one of the authors of the PurpleI2P C++ router rewrite (source code here).
Those don't do anything to prevent this issue. Once you have a public forum, that anyone can join and see the copyright infringement occurring, then the harassment of the server operators begins. It's not like a Riot operator cannot ban a certain channel or something, it's very transparent to server operators which channels are which regardless of the "end to end encryption".
To my knowledge, only tools like Freenet and Zeronet have solved the issue of censorability or single points of failure. They do it through true decentralization, but you run into issues of spam prevention/DDOS prevention etc with them. I am a Freenet developer personally, and one of the I2P C++ re-implementation programmers - see https://i2pd.website/ / https://github.com/PurpleI2P/i2pd/ for more info on that re-write. I am planning to launch a better hardened Zeronet fork with I2Pd instead of the Tor software router (because I consider Tor's routing protocol insufficient for what Zeronet tries to do, I also consider Zeronet's content distribution system insufficient for true decentralization though).
There's also the speed issue of Freenet/Zeronet. To the best of my knowledge, I am the only person to present a solution for fast, uncensorable networks. Unfortunately I've not been able to secure investments for it.