Specify NLS-Settings during Oracle installation under Windows
From the Oracle forums:  https://community.oracle.com/thread/777001

It appears that NLS_DATABASE_PARAMETERS is essentially a permanent copy of the values in NLS_INSTANCE_PARAMETERS at the time of database creation and cannot be changed later.  Reasoning given in link above is that NLS_DATABASE_PARAMETERS is used by the data dictionary to validate CHECK constraints and changing these parameters could violate those constraints.

NLS_LANGUAGE and NLS_TERRITORY need to be set to the desired values in your parameter file at the time the CREATE DATABASE statement is issued for the values to be stored in NLS_DATABASE_PARAMETERS.