From what I can see I have then sistem regional settings set to slovenian, plus I have the dafault sistem locale set to slovenian and also the default OS locale. I have everything that is possible set to slovenian. My windows are in english language if this plays a role.

If helps this what I get if I guery nls_session_parameters and nls_instance_parametres tables

select * from nls_session_parameters;
PARAMETER VALUE
----------------------------- -----
NLS_LANGUAGE SLOVENIAN
NLS_TERRITORY SLOVENIA
NLS_CURRENCY SIT
NLS_ISO_CURRENCY SLOVENIA
NLS_NUMERIC_CHARACTERS ,.
NLS_CALENDAR GREGORIAN
NLS_DATE_FORMAT DD MM YYYY HH24:MI:SS
NLS_DATE_LANGUAGE SLOVENIAN
NLS_CHARACTERSET UTF8
NLS_SORT SLOVENIAN
NLS_TIME_FORMAT HH24:MI:SSXFF
NLS_TIMESTAMP_FORMAT DD.MM.RR HH24:MI:SSXFF
NLS_TIME_TZ_FORMAT HH24:MI:SSXFF TZH:TZM
NLS_TIMESTAMP_TZ_FORMAT DD.MM.RR HH24:MI:SSXFF TZH:TZM
NLS_DUAL_CURRENCY SIT
NLS_NCHAR_CHARACTERSET UTF8
NLS_COMP BINARY

select * from nls_instance_parameters

PARAMETER VALUE
----------------------------- ----------
NLS_LANGUAGE AMERICAN
NLS_TERRITORY AMERICA
NLS_SORT
NLS_DATE_LANGUAGE
NLS_DATE_FORMAT
NLS_CURRENCY
NLS_NUMERIC_CHARACTERS
NLS_ISO_CURRENCY
NLS_CALENDAR
NLS_TIME_FORMAT
NLS_TIMESTAMP_FORMAT
NLS_TIME_TZ_FORMAT
NLS_TIMESTAMP_TZ_FORMAT
NLS_DUAL_CURRENCY
NLS_COMP