add a child language dynamically

Yes there is a dynamic creation form in the sample project that shows how to merge two languages programmatically. I think there is a help topic on this too.

Yes you can use anything in our test project. Which files you are indicating that you wish you were part of the built-in package? Most of the things in the sample project are intended to be customized further by you, and/or used for learning purposes.

Thanks - I looked at the sample project and there is an example exactly for what I asked.

As for your question - I think it is really good design that the language definitions are configurable and it is possible to define a new language. But if I use the c# xml definition and syntax code file I have to include it in my projet and do some ugly stuff (like changing the SyntaxLanguageTypeName) and next time when I get a new version of the syntax-editor I will have to update these files. It will be much better if these files will be part of the package somehow.