A compiled NIB file is a NIB file that has been compacted to take less space on the disk but that cannot be localized anymore. If this happens, contact the developer of the NIB file and ask him to send you the non-compiled version of the NIB file.
In Xcode, under
Project > Build Settings, go to the
Interface Builder XIB Compiler - Options section and make sure
Flatten Compiled XIB files is turned off
(IBC_FLATTEN_NIBS=NO). Ensure that the targets of the project
inherit the same parameter value.