update language list in openstack_dashboard settings.py

Imported openstack_dashboard/settings.py from merged
change I0c378e885efc4ecdafdd5d6b027a514a5af5bb2f. The
changes in openstack_dashboard/settings.py should be available
in master.

Change-Id: I116927c5c5d2e45e2b481369eba4e79ce7ffb34a
Merge "update language list in openstack_dashboard settings.py"