(I'm completely naif on this subject, maybe my question doesn't even make any sense)
So likely we will still have C/C++ for the low level, low latency, and then for higher level, well whatever you want, including javascript.
For example, ROS [0] have various bindings available python, lisp, (also ruby I believe), etc.
As Seren said, C is pretty much defacto at the moment. C has a fairly large community. What would be gained by using Erlang? My understanding is that Erlang is geared toward distributed systems. I can absolutely imagine an massively distributed control system would benefit from Erlang. If you think of 'robotics' like cars where there is essentially a different robot for each control, maybe Erlang is a good fit. If the device is going to have a single CPU, maybe not so much.
It really depends on the application and the architecture, but to me, Erland isn't a natural choice.
https://www.youtube.com/watch?v=96UzSHyp0F8
On the Elixir side of things, there's something like the Rails of embedded development in the making, a project called Nerves. This is a recent presentation on the project:
Justin Schneck - Enhanced Embedded Systems with Nerves (ElixirConfEU 2016)