There are some locales missing in https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Bundle/EzPublishCoreBundle/Resources/config/locale.yml (LU, AT, etc), compared to the list of existing ISO locales. Please add them.

Ref:
https://en.wikipedia.org/wiki/ISO_3166-1
https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes