Languages and Languages
You mixed a lot of different things up there.
F# is .Net's version of OCaml, an old and traditional functional programming language.
Go targets mainly system programming. It is an alternative mostly to C.
Scala and Ceylon are JVM languages, though Scala released its first version 8 years ago, and it is now on version 2.9.0, with a proven record of success while Ceylon has yet to release its first version.
Ruby is another language that is as old as Java, and has revolutionized web programming with Ruby on Rails... five years ago. There's a wide array of tools written in Ruby, and used in Linux and BSD servers -- FreeBSD's package tools have been written in Ruby for over a decade, for instance.
In fact, Python is not particularly older or more popular than Ruby -- it just attracts different crowds. So to call Ruby a "new" language and Python a "tried-and-tested" is non-sense.
So, my advise is that you actually learn a bit more about what's actually out there, before you even consider learning a new language.
As for learning a new language, it depends a lot on what you wish to accomplish and what your usual expertize lays.
If you are a .Net developer, you should definitely learn F#. Chances are high that interfacing with F# code will become common.
As a Java developer, the best bet is Scala and Groovy. Groovy is close enough to Java that it will hardly feel like learning a new language anyway, but while it is useful in some places, it can never replace Java.
If you are a Python developer, Ruby fits a similar niche, but is unlikely to be attractive if you think the Python way is the Right way.
And if you just want to stretch your horizons, learn Haskell.