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It depends on your needs and what you are going to develop in the future. Try to learn the basics of all these languages and then focus on the language you like the most. Good luck!
If Java is "rather slow" for you then of course C++ is your only option. So your apps won't use virtual machine (JVM) as an environment. You will be developing native (desktop/servers) applications.
Python might too hard for you because of no bracket and semicolon So Java and c++ is enough (IDK how to python)
As you already learned Java, I prefer Python for the next rather than C++. Python is somewhat different from the other two and, importantly, it is much easier to learn. Then compare by yourself! Just hearing may not make sense unless you already experienced other languages.