- XHTML (the latest "dialect" of HTML, because you need to be able as a programmer to integrate with internet
- Turbo pascal (only because this is the language with most books/tutorials/articles out there and you learn a very structured and meaningful language)
- Java (This producers more powerful code)
- Perl (is in use all over)
- LISP (just for the satisfaction of master it)
- C++ (the most powerful and accurate language there is. However you will have to do a lot of debugging, which you will have learnt to master in the previous languages)
After you have mastered these most commonly known programs, you should be able to learn a new one just by learning the syntax in 3-4 days tops
A response to the list above:
"Check out the courses offered from any reputable institution (read college/university NOT Technical Institute) and you will see that the FIRST language they have you learn is...drum roll please...C++. Why? Because C++ allows you to learn in a gradual manner, building upon the procedural roots and previous lessons, until you are able to do object oriented powerful programs (and some quite academic such as traversing a binary tree using doubly-linked lists - something you could not do in any language that does not have pointers and pointer mathematics). You may never need, itrw, to build a system using binary trees and doubly-linked lists, but once you have mastered them you start to see more possibilities when you are given an assignment from you boss."
Other languages and environments to consider - Django (Python), PHP, SQL, Lasso, Cold Fusion, Ruby on Rails, Visual Basic, DHTML, ASP, C#, Java, XCode, iOS, Android
For cross-platform, it seems C++ and Java are the best options. Or focus development on web-based applications.