That's provably untrue. If you mainly write modules for the ejabberd server, indeed erlang might be on the menu, but that's very specific. If you develop on the client-side, pretty much all mainstream languages (JS, Python, C/C++ w&w/o Qt, Java, Go, rust, C#, …) have decent and independently well-maintained libraries to interact with XMPP. On the server-side, prosody (Lua) is as big (if not bigger) than ejabberd. And there are Openfire (JVM) and other implementations as well. Erlang is definitely not as unavoidable as you make it seem.