how to change nls_language in nls_instance_parameters
Example below on how to update this:

[oracle@mydbserver dbs]$ unset LANG
[oracle@mydbserver dbs]$ sqlplus "/ as sysdba"

SQL*Plus: Release 12.1.0.2.0 Production on Fri Jan 27 13:18:26 2017
Copyright (c) 1982, 2014, Oracle.  All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SQL&gt; SELECT sys_context('userenv','language') from dual;

SYS_CONTEXT('USERENV','LANGUAGE')
--------------------------------------------------------------------------------
BRAZILIAN PORTUGUESE_BRAZIL.AL32UTF8

SQL&gt; quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

[oracle@mydbserver dbs]$ unset NLS_LANG
[oracle@mydbserver dbs]$ sqlplus "/ as sysdba"

SQL*Plus: Release 12.1.0.2.0 Production on Fri Jan 27 13:18:51 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SQL&gt; SELECT sys_context('userenv','language') from dual;

SYS_CONTEXT('USERENV','LANGUAGE')
--------------------------------------------------------------------------------
BRAZILIAN PORTUGUESE_BRAZIL.AL32UTF8

SQL&gt; quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options


This is where I edited the init and spfile - you might want to take a backup !!

[oracle@mydbserver dbs]$ ls
hc_scpp.dat  init.ora  initscpp.ora  lkSCPP  orapwmydb  spfilemydb.ora  teste.ora


edit initscpp.ora and spfilemydb.ora with the values you want for the NLS parameters
Then I proceeded to restart

[oracle@mydbserver dbs]$ sqlplus "/ as sysdba"
SQL*Plus: Release 12.1.0.2.0 Production on Fri Jan 27 13:25:30 2017
Copyright (c) 1982, 2014, Oracle.  All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SQL&gt; shutdown
^CORA-01013: o usuario solicitou o cancelamento da operac?o atual


shutdown was slow so I [ctrl+c] and tried to force restart then restart normally !!

SQL&gt; startup force
ORACLE instance started.

Total System Global Area 2,0724E+10 bytes
Fixed Size                  3158000 bytes
Variable Size            3070230544 bytes
Database Buffers         1,7645E+10 bytes
Redo Buffers                5230592 bytes
Database mounted.
Database opened.
SQL&gt; shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL&gt; startup
ORACLE instance started.

Total System Global Area 2.0724E+10 bytes
Fixed Size                  3158000 bytes
Variable Size            3070230544 bytes
Database Buffers         1.7645E+10 bytes
Redo Buffers                5230592 bytes
Database mounted.
Database opened.
SQL&gt; quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
[oracle@mydbserver dbs]$ sqlplus "/ as sysdba"

SQL*Plus: Release 12.1.0.2.0 Production on Fri Jan 27 13:31:17 2017

Copyright (c) 1982, 2014, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options

SQL&gt;  SELECT sys_context('userenv','language') from dual;

SYS_CONTEXT('USERENV','LANGUAGE')
--------------------------------------------------------------------------------
AMERICAN_AMERICA.AL32UTF8

SQL&gt; quit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production