Assuming your API is relatively small (at most 10 classes with 10-20 methods each) I would write a wrapper using C++/CLI that would be accessible to a C# program via a DLL file that could be linked to the project in Visual Studio. For a larger project, please provide details of your API via private message and I will update my quotation. I have 15 years of experience as a professional developer, 10 of those working with .NET. I have completed large projects using C++/CLI wrapping existing libraries before. I am also a native English speaker, so communication should not be a problem between us.