Manual:$wgDjvuToXML/en

Details
Path of the djvutoxml executable.

This works like  except much, much slower as of version 3.5. For now it is recommended that you use djvudump instead. The djvuxml output is probably more stable, so this recommendation may be reversed once they fix the efficiency problem. 

To enable the rendering of DjVu files, both $1 and this setting must be set. Alternatively you could set $1 instead of $2. (If both $1 and $2 are set, only $1 is used.)