All the free programming languages can be coded to be portable. Also it should include the run-time environments for each operating system in the market. This will be much useful for the programmers when they need to use a public computer. They can create programs in the language they like. And they can execute it from the run-time environment with the portable program. The preferred languages are: Java, Python.
I do like the idea of having portable run-time environments but you can't over look Perl in this matter as well.