How to change NLS_LANGUAGE system level

I do the followingSQL> alter session set NLS_LANGUAGE='GERMAN';

Session altered.

SQL> show parameter NLS_LANGUAGE

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
nls_language                         string      GERMAN

Then I do the following
SQL> alter system set  NLS_LANGUAGE='GERMAN' scope=spfile;

System altered.

SQL> STARTUP FORCE;
...........................................
SQL> show parameter NLS_LANGUAGE

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
nls_language                         string      ENGLISH

Why it's not reflected at system level? I check the spfile and I see the below
*.nls_language='GERMAN'

Thanks