The whole point is you learn and type it.
If you make an in-game mod it can then be read by anyone with ease and it loses its edge. Learning it means only people who have the patience or ability to learn it can read it. Making a mod means anyone, even some newbjob who wants in on your chat, can and will. Don't kill it already. >:I
We wouldn't pass out the code.

In fact, remember me mentioning the one Jetz has in Age of Time? It works like this?:
{{3933|%&hGfkdlde:?>}} The first number indicates the index in a preset jumbled array, and after the | is the text. Their games find that number, apply it to the index, then translate the text. It's a very nice system because the only real way to decipher it is months of trial and error, or having their entire array.