We just added support for additional programming languages:
AppleScript, COBOL, ColdFusion, Haskell, Modula-2, Modula-3, OCaml, R, Rebol, SML, and VHDL. They now appear in the language drop-down on the Advanced Code Search page
They also explain that you can search for any language you want by using the "file:" operator.
If your language of choice isn't on there, you can still search for code written in that language. Just use the the "file:" operator to restrict your search to files with the right extensions. For example, you could restrict your search to files with a .zz extension with a query like:
Or, you could restrict to multiple extensions, for example to .x and .abc with something like:
hello, \world file:\.(x|abc)$