Is nvarchar 0-indexed?
This is quite clearly explained in the documentation. The value in parentheses indicates the string length. So nvarchar(2) has a string length of 2.

https://msdn.microsoft.com/en-gb/library/ms186939.aspx


  nvarchar [ ( n | max ) ]  Variable-length Unicode string data. n
  defines the string length and can be a value from 1 through 4,000.