Why are national characters not displayed correctly?

Version 3.5.1:
To get national characters to be displayed correctly
both the character set and national character set parameters in Oracle
must have the same value, if running on Oracle 8.1.7.
Both parameters are set during the installation,
but national character set can be changed later on (it is NOT an init.ora parameter!).
To change national character set run the following SQL statement:
update sys.props$ set value$ = '' where name = 'NLS_NCHAR_CHARACTERSET';
Another solution is to use Oracle 9 client (or later),
i.e. on the server running IFS Application Server (FNDAS).
But the client machine (the one running FNDAS) has to set NLS character set to UTF8, otherwise national characters will not be shown correctly in error messages.
If FNDAS servers are started from a command script,
it is enough to set a value of NLS_LANG parameter at the beginning of the script, e.g.:
set NLS_LANG=SWEDISH_SWEDEN.UTF8
But if the servers are run as Windows services,
it can be necessary to modify the parameter in Windows Registry entry, e.g.: HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0
Note that the key can differ if running several Oracle Homes.
Version 3.6.0:
Depending on Oracle version some parts of the description above can be also valid for the node running IFS Extended Server (FNDEXT).