Either of these: - Elixir - Haskell - Ada Are all unique and quite enjoyable to learn. Each of them has challenging new concepts that are amazing once you g

Either of these: - Elixir - Haskell - Ada Are all unique and quite enjoyable to learn. Each of them has challenging new concepts that are amazing once you get your head around them (and a bit painful beforehand). Each one will teach you something new and valuable. Ada has an incredibly advanced concurrency model that blows everyone else out of the water. It is also incredibly safe -– this is the language that powers airplanes and spaceships (and missiles). Beware: after using Ada, you will hate the concurrency primitives of other languages. Haskell is a great and enjoyable introduction to functional programming with concepts that can be taken anywhere. Elixir can create extremely robust software through the "let it crash" philosophy and supervisor tree structure. Also a great intro to highly distributed systems, probably the only language where I found the lack of types to be an advantage. The concepts have been replicated in other languages (e.g. Akka, various actor frameworks)