I found that article: https://medium.com/@gzanon/no-end-to-end-encryption-does-not...

I tried to read data transmitted between the facebook messenger app (on iOS) and facebook server but it's encrypted and if you set up a mitm proxy it refuses to transmit. Even if you trust the mitm proxy certificate in the OS settings.

XMPP with OTR is exactly this. Facebook messager used to be compatible with XMPP.

Not exactly. I rather dislike XMPP's design, and what I'd like to see is something not only decentralized (relying at most on a DHT seed), but supporting group chats with trivially-expirable keys. My limited exposure to OTR suggests it only reliably supports one-on-one exchanges.