Add language in C#

What language did you have in mind? I can only assume that you'll be working in Visual Studio, or maybe a shell, but it might not make any difference. With C# you're pretty much limited. As to what you can do and on what platform. From C# you can also use Visual C# and .Net, and probably Java Script (No Java though). It gets pretty slim after that. There are others, but not those in common use, such as J# or Visual J#. I think that even with Visual Basic, it would be one or the other, but not together.
A good place you to start (and a handy reference too) would be the C# Programmer's Reference, found at: http://msdn2.microsoft.com/en-us/library/618ayhy6(vs.71).aspx

I hope that helps. -d