Yes, mixing languages is a pro's version of this. Earn 10 points for every language and 20 points extra for every interface between them. Macro languages like XML do count.

Additionally do some build system breakage with automatically partially generated code for extra credit.

Of course if you create some DSL or XML, never include schema or any kind of documentation that is not the parser.

And absolute worst: include optimizrd binary only code - no documentation and sources. Reverse engineering is fun!

nah. R is actually not bad. i would go for nodejs. or any sort of dependency injection, so no one would ever know what method behind an interface is being called. not to mention kdb+, which is write-only by design.