Erlang's core concept of concurrency seems like something that'd be better suited as a library and app server than a whole language and runtime.
I've yet to hear of any Erlang-specific magic that cannot be implemented inside another language.
There's a reason Stackless Python's actors aren't just a library on top of Python.
Those are the first two "ghetto" hack solutions I can think of that wouldn't require significant code changes on a going-forward basis.
It's like the kernel protecting memory so applications can't overwrite each other. Sure, applications could just write to their own memory, but nobody actually trusts that model[1]. Instead, they want something below that level enforcing good behavior.
1. Obviously, virtual memory adds a wrinkle to this that kind of forces kernel protection, but even if we had literally unlimited RAM, we would still implement kernel protections on memory.
But what you can't (practically) implement yourself in other languages is all the professional care and maturity that have gone into the whole package over its long history. AFAICT, Erlang/OTP is much more than just a library.
It's the expressiveness at the language level that is really the "magic". For example, doing the equivalent of OO is not intuitive in Erlang, but completely possible (actually easy, but it looks...wrong) whereas it's supported by every Java tool. By the same token, pattern-matched message passing, lightweight green threads, and hot code deployment are primary concepts in Erlang.
With sufficient effort, you can have the equivalent of no shared mutable data.
What you cannot have is completely separate heaps, so that if one thread crashes for whatever reason it doesn't take your application down.
Also, good luck trying to find a garbage collector that supports completely separate heaps that isn't a direct copy/near-identical implementation of the BEAM[1] VM's GC.
[1] The virtual machine that is the stock VM for Erlang. (In fact I don't know of any others but I have never looked.)
Now it's even easier with ESBs. Write a ten-line grails service to expose a bin-packing facility with Drools and then never touch it again.
