select userenv('language') from dual

Oracle/PLSQL: UserEnv Function

In Oracle/PLSQL, the userenv function can be used to retrieve information about the current Oracle session. Although this function still exists in Oracle for backwards compatibility, it is recommended that you use the sys_context function instead.

The syntax for the userenv function is:

userenv( parameter )

parameter is the value to return from the current Oracle session. The possible values are:

Parameter	Explanation
CLIENT_INFO	Returns user session information stored using the DBMS_APPLICATION_INFO package
ENTRYID	Available auditing entry identifier
INSTANCE	The identifier number of the current instance
ISDBA	Returns TRUE if the user has DBA privileges. Otherwise, it will return FALSE.
LANG	The ISO abbreviation for the language
LANGUAGE	The language, territory, and character of the session. In the following format:      language_territory.characterset
SESSIONID	The identifier of the auditing session
TERMINAL	The OS identifier of the current session

For example:

userenv('ENTRYID')	would return FALSE
userenv('LANGUAGE')	would return 'AMERICAN_AMERICA.WE8DEC'