You should learn as many languages as it takes to satisfy your intellectual curiosity. If you want to cover the bases: an assembly language (I recommend ARM), an unsafe "high level" language like C or C++, a high level statically typed object oriented language like Java, a dynamically typed one like Smalltalk, a pure/lazy functional language like Haskell, a strict/impure functional language like ML, a logic language like Prolog or Mercury, a concurrency focused language like Erlang or Go, and a Lisp for the sheer power/terror of high level metaprogramming.
For your career, learn one or two languages extremely well, to the point you could write it from scratch given the time.
You should learn as many languages as it takes to satisfy your intellectual curiosity. If you want to cover the bases: an assembly language (I recommend ARM), an unsafe "high level" language like C or C++, a high level statically typed object oriented language like Java, a dynamically typed one like Smalltalk, a pure/lazy functional language like Haskell, a strict/impure functional language like ML, a logic language like Prolog or Mercury, a concurrency focused language like Erlang or Go, and a Lisp for the sheer power/terror of high level metaprogramming.
For your career, learn one or two languages extremely well, to the point you could write it from scratch given the time.