Forum: RForum Error when integrating rforum to my application

I tried to integrate rforum to my application using engine. In rforum 
there is a file called localization.rb where function 'l' is defined. 
Even though I copied those file to the plugins folder of my application 
under folder 'lib', i was not able to access that function.
Do anyone have any suggestions regarding this issue? If there is any 
suggestions it will be very helpful for me..