When should Python be used?
Python is a light, easy to use scripting language. Though it has its shortcomings for delivered software, it is probably one of if not the fastest way to turn your idea into a functioning program, while also having immense functionality for almost any application. Python is fantastically versatile, and its ease of use makes it a great choice with application in just about every field that uses programming in some way, from proofs of concept to in-house tools used in major companies to test their own products. My personal favorite thing about Python, though, is that it's easy to understand, easy to learn, and fantastic to mess around in and toy with new ideas, making it (in my opinion) one of the best languages for learning and improving your understanding of programming.
Why is Java important to know?
While programming and security puritans might have you believe Java is the work of the devil, Java is THE programming language of business, being by far the most widely used language for software in all things. While it has its points of criticism, it is higher level than C and C++, easy to start a project with, and still maintains fantastic speed, with runtimes comparable to that of C++. Alongside its strengths in specific domains such as in servers, the overwhelming abundance of example code you can find online from other peoples' projects makes it probably the single most marketable programming language to know.
Why is C++ still relevant and important to learn after 20 years of standardized use?
Though the world of computers is always evolving, C++ can still be counted on as one of if not the most versatile programming language. With support for multiple programming paradigms and the ability to use, share, and import libraries with myriad functionality, C++ has the capacity to do just about anything in the computer world, though that could be argued of nearly any programming language, given the patience and the know-how. Where C++ really shines though, is that at its base, it compiles relatively straightforwardly and predictably to machine code, which gives a great programmer all the tools needed to make extremely efficient code, while also not being unreasonably complicated or overbearing like C tends to be. Perhaps C++ is not as important now as it was back when it was invented, and a megabyte was a decent chunk of your computer's memory, but for complicated functionality that needs to be run in real time, C++ is a powerful ally that should not be scoffed at - and even if you think you'll never need such efficiency, learning about efficient code is never a bad idea.