Is there a way to ensure that other .NET languages will interoperate with my C# classes ?
The most important thing would be for you to use the CLSCompliantAttribute. This prevents you from inadvertently using non CLS compliant features in C#.
There are a few pretty obvious rules that I can mention here. Note, this list is not exhaustive. I just wanted to point our some of the rules to give you a feel of what CLS compliance is all about.
Read the article Cross Language Interoperability for more information.