The first thing I did was to see if there were questions or related that referenced F# (which is my language of choice).
Typing "F#" into the search box returned more or less every indexed item on the site. Typing "C#" had a similar effect.
Trying the "tags" box was slightly more successful - it turns out the tag is "dotnet-fsharp" (and there are no items tagged with "dotnet-fsharp"). Similarly C# turns out to be "dotnet-csharp" - and there are items tagged that way.
Whether these are the "right" tags is an open question, but in terms of discoverability something better needs to be done (either tag with F# C# & VB or do magic in the back end to achieve a similar result)