Oracle, Stored and External procedures
Stored Procedures and External Procedure are distinct ones. 

Stored procedures are stored in database and used from there. You can write them in different languages. Also note that you can pre-compile PL/SQL instead of interpreting


SQL/PL-SQL , most common 
Java 
.NET only in windows environment.


External Procedures are external functions/procedures in Operating System. You write a stored procedure in PL/SQL, use  call specification to call other languages in operating System. This potentially gives you power to call any function in other languages. Following usages come to my mind.


Use a Data Mining algorithm which is not implemented in Oracle Data Mining
Use ftp function to transfer files to another server
Use a graphic functions of Gnu Plot to create graphics and store them in database for later use.


These usages in my opinion are extreme and unnecessary. All of them can be accomplished with application programs. Nowadays nobody uses database as it is. There are always applications built using Java, .NET, PHP etc. Whenever possible, these other languages should be used in application.