Partly reverts d7a5ec62

An empty locale was treated as LANGUAGE_NONE, effectively being
interpreted as absence or undetermined or multiple or all depending on
context. Restore this behavior as it was an undocumented feature of the
API.

Change-Id: I256b352961f09e41cadb3e44c9ef01ee7677fd31
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>