I have a table with nvarchar field (MS SQL Server 2008 R2). For testing, this code works fine:
Update [Screenshots] set name=N\'Значение\' where id=230246
Are you sure that formData.Get("description")
returns UTF-8 string (that it isn't converted somewhere)?
What is your approach in entity framework? Code-first/Design-first/Database-first?
Try to remove database and recreate - remove database and then in designer right click -> Generate database from model...
Get Entity Framework Profiler from Nu-get package manager and see what query is sending to database.