I tried to migrate to the new localized string catalogs. But after this I can't build the app anymore. The error message stated something about an "old" .string file... but I checked all directories and there are no old .string files...
Anybody a hint how to go further?
And this is how the directories look after migration ...
I believe that the error is referring to the presence of InfoPlist.strings, Localizable.strings and LocalizableDict.strings in Base.lproj directory.
I could be wrong, but if my memory serves me right, Base localizations for .strings files are not supported (it was intended only for things like Storyboards although I never really used it so I might be mistaken).
My guess is that the migrator only migrated the .strings/.stringsdict from actual language directories and as a result, Base.lproj was left untouched.
Try removing those files and see if the issue persists. Note that you might need to manually import the contents into your new Strings Catalogs if they weren't already covered by your development language.