I think you can follow the guidance in Akihiro Motoki to add more languages:

"Yes, Users can customize the language list by editing OpenStack Dashboard setting files (settings.py).
Note that OpenStack Dashboard has two settings files: settings.py and local_settings.py,
local_settings.py contains configuration parameters which users usually configure, and
settings.py contains parameters which are less required to configure."

From http://lists.openstack.org/pipermail/openstack-i18n/2013-September/000131.html.

Regards
Ying Chun Guo (Daisy)

Tom Fifield <tom@openstack.org> wrote on 2013/09/28 21:59:37:

> Tom Fifield <tom@openstack.org>
> 2013/09/28 21:59
>
> To
>
> Ying Chun Guo/China/IBM@IBMCN,
>
> cc
>
> openstack-i18n@lists.openstack.org
>
> Subject
>
> Re: [Openstack-i18n] How to use partially completed languages for
> devstack horizon?
>
> Thanks! I followed this (and added one update), but I don't see my
> language in the list. *reads the code*
>
> Regards,
>
>
> Tom
>
>
> On 28/09/13 23:22, Ying Chun Guo wrote:
> > Take a look at this wiki page to see if it can help.
> >
> > https://github.com/OpenStack-I18n/Translation/wiki/Horizon-I18n-Test
> >
> > Regards
> > Ying Chun Guo (Daisy)
> >
> > Tom Fifield <tom@openstack.org> wrote on 2013/09/28 20:53:29:
> >
> >  > Tom Fifield <tom@openstack.org>
> >  > 2013/09/28 20:53
> >  >
> >  > To
> >  >
> >  > openstack-i18n@lists.openstack.org,
> >  >
> >  > cc
> >  >
> >  > Subject
> >  >
> >  > [Openstack-i18n] How to use partially completed languages for
> >  > devstack horizon?
> >  >
> >  > Hi i18n,
> >  >
> >  > I'm potentially giving a dashboard demo in Moscow next week, and thought
> >  > it would be cool if I could change the language settings to use our
> >  > almost-complete Russian translation.
> >  >
> >  > Does anyone have some easy steps I can follow to download the PO file
> >  > from transifex and then configure devstack to use it?
> >  >
> >  > Regards,
> >  >
> >  >
> >  > Tom
> >  >
> >  > _______________________________________________
> >  > Openstack-i18n mailing list
> >  > Openstack-i18n@lists.openstack.org
> >  > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-i18n
> >  >
> >
>