[memracom]

The only one on your list worth learning is Erlang. However, there is a JVM language called Clojure that is a form of LISP and is very worthwhile, but the main reason for learning Clojure is not that it is a form of LISP, but that, like Erlang, it deals with the issue of how to build highly scalable concurrent applications. A less exotic path to the same thing would be to use Groovy along with the Apache Camel library. Or to use Scala along with Akka which essentially is an implementation of Erlang's actorsystems in Scala.

J is an interesting suggestion, but I think that it is best learned along with another more conventional functional language such as Scala or Erlang. J was really innovative back in the 1960s when it was called APL, but now it is a bit of a niche language although still highly useful for financial applications.