Quite often, in the development process, developers put the localizable strings within the code (resource files, I18n lib, etc).
Very often, developers make typo, gramatical, semantic errors. Even if the strings are provided ;o)

Don't you think it could be valuable to upload those strings within a 'neutral' locale as the reference language ?
Then, if default language is 'en', you add an 'en' locale in order to correct things.

Another feature is that the neutral locale is the source of thruth of what is really used within the app.
The 'neutral' locale should be readonly and only updated by upload from dev environnement.