I exported the localization xliff file with no errors. I localized the file, imported back to Xcode and ran the app. Everything was good.
I exported the localization xliff file again for a second-round localization. I found many keys duplicated and they are not translated, of course. Why did this happen? Is it a bug in Xcode? How to work around it?
Side Note that might be helpful: I have test targets.
As I expected, the Export XLIFF file includes localisation strings in test targets too. I am using Xcode 6.2 now and still there is no way to exclude test targets from this process.
I had to open the file using a text editor (for example, TextEdit) and remove all the localisation nodes for test targets.