Sitefinity does allow you to use VB.NET as your development language.for the purpose you have to convert your sitefinity project to be VB.NET project as by default it is created as C# project. For the purpose follow the guide in this
Note you can only use VB.NET or C# in your Sitefinity projects as mixing them will not work.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items