If like with our apps you have a team of localizers translating your applications then -- unless your project is open source -- your localizers need to be able to open your NIB files.

If you created your project in Xcode 3 you'll notice that there are no longer any NIB files, since Xcode 3 uses text-based XIB files for better integration with source code management software such as Subversion. These XIB files are converted to NIB files during compilation, but by default the flattened NIB files that can't be opened by Interface Builder.

For your localizers you'll need to create a compiled application with unflattened NIB files:

1. In Xcode select your build target and choose File > Get Info
2. Click Build
3. Select the configuration you want to send your localizers. I recommend not to use the release configuration; instead, use either the debug version or create a dedicated configuration.
4. Deselect the "Flatten Compiled XIB Files" option
5. In newer versions of Xcode you also need to deselect the "Strip NIB Files" options