I am very agnostic for what is concerned programming languages.
C++ is a must for any production ready code, such as online search code (and if you use STL and boost you have a rich lib set). C# is useful for offline code, due to the inner rich set of lib set. Some people loves Java for this stuffs (e.g. Lucene, Hadoop, and other very good enviroment). Then, you you are in the scripting coding for fast and dirty prototyping you may want to use python (which is good for strong typed system) or perl (which is good for the vast set of modules, see CPAN).
So, I need to write an HTTP proxy for filtering some content. What is my choice? In this case, perl with HTTP::Proxy module, which allows me to filter both headers and content.