There are two things, the right language, and the right library. Often the library available to perform a task dictates the language.

I think also that your roladex can be a lot smaller. Many languages have been subsumed by later ones. There are very few places where you would choose Algol over C++ or Basic over Perl for example. There are many many languages, a lot of which have been created for a very narrow range of application.

In practice knowing a good and well supported scripting language (Perl?) and a good and well supported general purpose language (C++?) and the "languages" associated with particular problem domains that you are interested in (MatLab, HTML, ...) will get you where you want to go in pretty short order. By well supported I mean that you should find the language available most places that you go and that there is a lot of good third party code available in librarys of various sorts.

Appart from anything else, knowing a small, but diverse set of languages well will make it so much easier to learn and use anything else that you may be forced to pick up for a particular project, that in practice your half dozen language roladex actually encompases all the languages that you are likely to need.