I suggest that you not explicitly include programming languages
in the set of languages to be covered by content-language.
One danger is that it starts to conflict with content-type.
Another is that there are sometimes different versions of a program --
one for English speakers, another for French, etc -- but all written
in C.
We've run into a similar conflict with the netlib mathematical software
repository (consisting mostly of FORTRAN and C programs and subprograms) --
which also happens to include more traditional literature like research papers
and documentation. Our experience with the use of the "language" field in our
bibliographic entry to describe both programming languages and human
languages, has been awkward at best. For example: when searching, it doesn't
work to restrict queries to items using "C" as a language, because that would
exclude the documentation (written in English).
Keith