Do we need this many? No. We don't need any. There are many reasons new languages get created, but very rarely does an old language ever die. Erlang was created out of a need for reliable, scalable, multi-threaded programs that could withstand failure. D (and arguably Rust to an extent) was created due to perceived failures in C++. Scripting languages weren't even practical for real programs for decades, so of course people created less verbose languages when they got the hardware.
In addition, new languages are being created for research (ML, LISP 1.0, Racket) and for fun. Not many of either of those categories catch on, but there's enough volume of them that they still proliferate.