Replace "Junk" by "spam"

In the code of Roundcube, there are many references to a folder named Junk but I don't see any such folder. When I create a folder named Junk, it gets a special icon but it doesn't server any purpose (no filtering). Now my spam assasin delivers junk mail to a folder named "spam" (this folder is created when spam arrives for the first time). Roundcube recognises this folder but doesn't subscribe to it, unless the user explicitly ticks it in the Settings Panel. Now how do I display the "spam" folder as default (like Trash etc) for all the users and how do I assign it the special "Junk" folder icon?