Localized OS X app refusing to run in the Base English localization

Question

I have a localized OS X app.
There are several languages supported, the Base localization is English:

When testing on Mountain Lion, the app behaves strangely.
It refuses to run in English, as if the localization was missing. (On modern OS X versions it works just fine.)

What could be the problem?

I tried duplicating the Base.lproj folder from the app bundle as en.lproj and the problem disappeared.
Is this a problem with Base Internationalization support in older OS X versions?

Answer 1

While I would love to have a better solution, in the end I have added a “run script” build phase that just copies Base.lproj to en.lproj in the app bundle.