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
See Oracle Database Reference for more information about NLS parameters, including valid values.