at the moment I´m doing some testing with my first localized application. See Screenshot.
In order to use localized text in a PopUpMenu on first use I´m using this to find out what system I´m on:
NSString *identifier = [[NSLocale currentLocale] localeIdentifier];
On a German system identifier returns de_DE, On an English system I get en_EN_POSIX.
On a French system I would expect to get fr_FR but unfortunately I also get de_DE.
Any idea what I´m doing wrong?

Make sure that this locale is set in the system preferences. Select language&text, then the region text and switch it to your region.