ORA-12705: Cannot access NLS

Hi,

On 19c7 on AIX

My database has :

AMERICAN_AMERICA.WE8ISO8859P15 and NLS_NCHAR_CHARACTERSET UTF8.

How can I verify that ORA-12705 comes from incorrect Oracle install or configuration?

I connect with system user in sqlplus (on the database sever then no network problem)and then:

SQL> ALTER SESSION SET NLS_LANGUAGE= 'FRENCH';

ERROR:

ORA-12705: Cannot access NLS data files or invalid environment specified

SQL> show parameter NLS_LANG

NAME                 TYPE    VALUE

------------------------------------ ----------- ------------------------------

nls_language             string   AMERICAN

SQL> show parameter ORA_NLSx

oracle$ env |grep ORA_NLS <== empty

How can I verify that it comes from