Add example of translating messages

[davidmalcolm]

I see README.md "Advanced topics" has

    Translations (TODO)

I'm breaking this out into an issue since I was looking at this in GCC's SARIF generation code and I think I'm probably misunderstanding at least one aspect of the spec, so a tutorial would be helpful. Feel free to steal the idea of using Pig Latin as an example "language" for localization.