Those C# developers who would like to write a DLL in C# for Metatrader instead of in C++ now have a path to that end. There is a very interesting article titled "Exposing C# code to MQL5 using unmanaged exports" that I've just read. I use MT4 (MQL4) instead but the idea is still valid.
Read/skim the article and read section 2.5 onward.
Exposing C# code to MQL5 using unmanaged exports - MQL5 Articles
Read the directions, then download the Template for C# "Unmanaged Export Library" and place the zip file in the right directory (by following the directions on that page):
C# Project Template for Unmanaged Exports
Load Microsoft Visual Studio 2010 (or Microsoft Visual C# 2010 Express) and select the "Unmanaged Export Library" template. Follow the code samples. Hope this helps somebody!
You can find sample code for creating a C# dll with the Unmanaged Export Library here including a download for the visual studio solution and the MT4 sample script.