The NLS_DUAL_CURRENCY option specifies a second currency symbol that takes the place of the letter U in a number format mode and is used primarily to identify the Euro symbol. (Note that when you want to identify the Euro symbol as the value of NLS_DUAL_CURRENCY, the instance character set must support that symbol.)
Within a session, you can dynamically modify the value of this option using the OLAP DML syntax show below or by using the SQL statement ALTER SESSION SET option = value.
TEXT
NLS_DUAL_CURRENCY= option-value
See Oracle Database Reference for more information about NLS parameters, including valid values.