If you don't know C, learn it. Its very different from python and java, but will give you a feel for whats going on "under the hood" so to speak in both those languages.
Depends on what you want out of learning a new language. If you want to become more familiar with the fundamentals of computers and how they work, C is the best option; if you want to learn a new paradigm and way of thinking, I recommend Haskell; if you plan on doing any web stuff, JavaScript is pretty much a must; and if you want to be at the forefront of new language developments, go for one of the shiny new languages like Go or Rust (I'm currently taking this route).
this is a questions asked quite often and i guess there is only one answer: what do you want to achieve? Do you want to make Web Apps, Mobile Apps, Desktop Apps, Games,... there are so many different directions you can go, that you should first answer the questions WHAT and then answer the question HOW and not the other way around.
I recommend doubling-down and focusing on Java. It'll help you get fundamental programming concepts down and will give you a strong foundation in object-oriented programming.<p>I recommend learning C after Java. It's much more difficult to learn, but your prior Java experience will help you pull through.<p>Note: this all depends on what you mean by "some" programming experience.
C or C++ (or both) and C#. This new languages like, Rust,Go etc you may learn after C or C++ (IMHO). It's because by using C programming language you learn much more how the computer/software works in background than using high-level ones. But don't give much of your time on it, if you aren't focusing system applications.
From a similar position I found scala was the best help professionally. It combines the best of both - lightweight syntax like python, but with strong typing and the java library ecosystem - better still, you can introduce it into a java project bit by bit.
C was trivial to learn, don't listen to them. I learnt that first, and it made learning other languages easy (most popular languages are modeled after C). Mobile is a hot market, so it'd be good to learn Objective C. Also, Javascript is another popular one. Then I hear talk of learning Haskell and Lisp "just because," but I don't do anything "just because."