Most languages can be compiled on most platforms (except Microsoft VisualBasic, which is Windows-only, as far as I know)... They will more than likely need modifications depending on the platform they are being compiled under, for example, different includes are needed on Unix/Linux to Win32. However, Java is truly platform independent, and the same code will work on any platform that the Java runtime is installed on.
Not that I'm trying to sell java here - I'm with you that C / C++ are the best, cause they're the most poweful, besides Assembler.