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From what I remember, Discord used Elixir for guilds (although, they use a lot of languages for a lot of things), so the more you know.
Who knows if they still do it though.
Of course, Discord cheated a fair bit by using a lower level language to circumvent Elixir's limitations.
Matrix will still be better than Discord though, because it actually supports end-to-end encryption, and you can install it on your own hardware.
Also, you don't have to rely on yet another unreliable tech giant.