Rewriting systems in another language can certainly be accomplished. If possible, doing it in bits and pieces will help it actually happen; if you do it as a single big switch, you have to work a lot harder to avoid the second-system effect.

In this case, you probably first start by switching your message queuing to Erlang (RabbitMQ), since you had a problem with that anyway; then you can expand outwards from there if it makes sense or makes you happy: job running in Erlang, webservices in Erlang, putting the data in mnesia instead of postgres, etc. You can do the same with any language, of course.