A few thoughts:
- The page you linked to explains pretty clearly how it's done
- If you are interested in learning a language, this is probably not the place to start
- Programing a single application in two or more languages is only marginally related to the linked document.
Still, in the face of all that, I'll try to give an example of how this works by analogy.
Suppose you need to work with a group of people on some technical task--ranking chess puzzles by difficulty or testing marshmallows for contamination or something. Suppose further that one of the people on your team speaks only Japanese, another only Portuguese, and the third only Esperanto.
Being blessed with the ability to speak all of these languages fluently, your best bet is to make up an artificial language specialized to the task at hand; this is called a Domain Specific Language, or DSL. It should have all the terminology you need to talk about knights and rooks or silicate nanoparticles or whatever for the task, and not much else. Teach this to each of your team members, and then you can give them all their instructions at the same time. They can talk to each other about what they are doing, ask for help (so long as it's related to something covered by your language) as if they all spoke the same language.
That's roughly what he's talking about.