ORA-12709: error while loading create database character set

Problem Description
While mounting oracle database it fails with ORA-12709 like below.

SQL> alter database mount;
alter database mount
*
ERROR at line 1:
ORA-12709: error while loading create database character set

Cause of the Problem
The error ORA-12709 is returned due to incorrect setting of environmental variable NLS_LANG
or ORA_NLS33.

Solution of the Problem
Check your NLS_LANG environmental variable by,
$echo $NLS_LANG.
If it is set to wrong value and your database character set is WE8ISO8859P1 then set by,
$export NLS_LANG=American_America.WE8ISO8859P1

Note that, For Oracle7 V7.3.2 version ORA_NLS33 environmental parameter is called ORA_NLS,
for Oracle7 V7.3.3 and V7.3.4 it is called ORA_NLS32,
for Oracle8 it is called ORA_NLS33 because of NLS libraries version.

When using both Oracle8 V8.x and Developer/2000 V1.6.1 in the same Oracle Home, ORA_NLS33 needs to be set to $ORACLE_HOME/ocommon/nls/admin/datad2k
The environmental variable along with database version is given below.
RDBMS 7.2.x -> ORA_NLS
RDBMS 7.3.x -> ORA_NLS32
RDBMS 8.0.x -> ORA_NLS33
RDBMS 8.1.x -> ORA_NLS33
RDBMS 9.X.X -> ORA_NLS33
RDBMS 10.X -> ORA_NLS10

After you set both parameters correctly login as sys user.

$ sqlplus '/ as sysdba'

SQL*Plus: Release 9.2.0.8.0 - Production on Sun Sep 26 00:40:18 2010

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.8.0 - Production

Shutdown and Startup the database.

SQL> startup force;
ORACLE instance started.

Total System Global Area 320300808 bytes
Fixed Size 734984 bytes
Variable Size 285212672 bytes
Database Buffers 33554432 bytes
Redo Buffers 798720 bytes
Database mounted.
Database opened.
SQL>