Scheme will teach you more about computer science than all of the rest of those languages put together. It's a beautiful language. (I taught some beginning programming labs in both Pascal, C, and C++. Pascal was wonderful. C was okay, execpt for the points you had to gloss over: Q:``Why do I have to put an ampersand in front of a string argument?'' A:``You'll find out next semester.'' C++ was awful. It's such a hodgepodge of language that it's hard to find any computer science in it. Perl would be even worse.)

As to its real-world application, there's scsh, if you're inclined towards sysadmin stuff. There's really no reason you couldn't write any application in it. It'd just be more difficult than usual to attach to external libraries, though far from impossible.