I localized a part of my application with creating a base.lproj storyboard and 3 string files for it. It was a month ago and after that I added new view controller to app, b
Finally, my solution was (rudimentary but effective) copy the previous translations and paste them in the a new file created by unchecking and checking the Localization language box.
This would be useful in some cases like mine when you have to change only one or two texts.