Some more information:
We started having this discussion during Fedora Globalization activity day at Tokyo Japan.

Progress we made is available in [https://docs.google.com/document/d/17LU-PmtuirbGd7wfxUuKTz7X6fsv82PVPgZaDELi4js/edit# summary document]

Pasting here again
git.fedorahosted.org/git/spin-kickstarts.git
We first tried with dnf-langpacks and successfully created English Livecd for f23.
We then tried to find if langpacks plugin worked but we found some issues in either network connectivity in %post of kickstart or actual fedora 23 repository.
We will check this bug tomorrow when we have Fedora 23 actually released and synced on mirrors.
* We checked only workstation live kickstart.

Changed has been proposed on this idea.
https://fedoraproject.org/wiki/Changes/LangpacksInstallationWithRPMWeakDependencies

We will test this in Fedora i18n test day. How it works. Once langpacks works perfectly it can help to create language spins easily.

it doesn't work (automaticaly) when installating from LiveCD :
Bug from alpha https://bugzilla.redhat.com/show_bug.cgi?id=1322246
wich is in fact a duplicate of https://bugzilla.redhat.com/show_bug.cgi?id=1319073
no solution implemented yet

Right. The respective Server and Workstation group need to be requested to add langpacks-* packages but we don't know whether adding these packages will pull any other packages in the composed iso. We need to estimate the increase in iso size. I will find some time to create first Server kickstart and generate iso from it.

Not planning to add this in i18n testcases, since present decision is pending on WG of server and workstation.

For Server WG, already emailed them https://lists.fedoraproject.org/archives/list/server@lists.fedoraproject.org/thread/TQOIVQEODLBOKF7XVBD5KW4E2AWYO7TV/

any specific update here?