I believe that's 'by design' that only stuff for your current locale gets installed (which in your case was American English), but we can get the scoop from yum-langpacks maintainer(s)

To install Italian language support, you need to either run yum in italian, or configure the langpacks plugin (/etc/yum/pluginconf.d/langpacks.conf).

These groups will be removed in a future release - having to hardcode all the language packages in comps just doesn't scale.

(In reply to comment #2)
> To install Italian language support, you need to either run yum in italian,

eg You could run "LANG=it_IT.utf8 yum update", etc to trigger
yum-langpacks.

Note that if your desktop is not running in Italian anyway
you probably won't be able to make use of the Italian language
packs (for Libreoffice, etc, etc), so if you really want this
for yourself you are better off running your desktop in Italian
anyway for this to be useful.

It is not very obvious but in gnome-control-center you can
change your desktop language to Italian and then restart
your desktop for it to take effect.

So to conclude, I think this is the expected behaviour
and this bug could be closed.

Are there any particular Italian packages you were after?

Could it be related tohttps://bugzilla.redhat.com/show_bug.cgi?id=830563  ?

I can see that 

comps-f16 has

  <group>
    <id>italian-support</id>
    <_name>Italian Support</_name>
    <_description/>
    <default>false</default>
    <uservisible>true</uservisible>
    <langonly>it</langonly>
    <packagelist>
      <packagereq type="conditional" requires="aspell">aspell-it</packagereq>
      <packagereq type="conditional" requires="autocorr-en">autocorr-it</packagereq>
      <packagereq type="conditional" requires="childsplay">childsplay-alphabet_sounds_it</packagereq>
      <packagereq type="conditional" requires="eclipse-platform">eclipse-nls-it</packagereq>
      <packagereq type="conditional" requires="gcompris">gcompris-sound-it</packagereq>
      <packagereq type="conditional" requires="hunspell">hunspell-it</packagereq>
      <packagereq type="conditional" requires="hyphen">hyphen-it</packagereq>
      <packagereq type="conditional" requires="kdelibs3">kde-i18n-Italian</packagereq>
      <packagereq type="conditional" requires="kdelibs">kde-l10n-Italian</packagereq>
      <packagereq type="conditional" requires="koffice-core">koffice-langpack-it</packagereq>
      <packagereq type="conditional" requires="LabPlot-doc">LabPlot-doc-it</packagereq>
      <packagereq type="conditional" requires="libreoffice-core">libreoffice-langpack-it</packagereq>
      <packagereq type="conditional" requires="man-pages">man-pages-it</packagereq>
      <packagereq type="conditional" requires="moodle">moodle-it</packagereq>
      <packagereq type="conditional" requires="mythes-en">mythes-it</packagereq>
      <packagereq type="conditional" requires="nqc-doc">nqc-doc-it</packagereq>
      <packagereq type="conditional" requires="tkgate">tkgate-it</packagereq>
    </packagelist>
  </group>


on the other hand has nothing in comps-f17 ?

  <group>
    <id>italian-support</id>
    <_name>Italian Support</_name>
    <_description/>
    <default>false</default>
    <uservisible>true</uservisible>
    <langonly>it</langonly>
    <packagelist>
    </packagelist>
  </group>

correct, f17+ uses yum-langpacks instead, and not comps conditionals anymore

any chance so that yum groupinstall "xyz-support"  will automatically run yum-langpacks as well?

In above case yum-langpacks will become backward compatible.

Unlikely, because (among other reasons) it would require a <lang name> -> <lang code> mapping.

Adding a 'langinstall' option might be simpler.

(In reply to comment #9)
> Adding a 'langinstall' option might be simpler.

Right.  Would that code live in yum-langpacks?

*** Bug 830563 has been marked as a duplicate of this bug. ***

> Unlikely, because (among other reasons) it would require a <lang name> -> <lang
> code> mapping.

Isn't that what the <langonly>it</langonly> tag in comps is for?

The implicat(In reply to comment #12)
> > Unlikely, because (among other reasons) it would require a <lang name> -> <lang
> > code> mapping.
> 
> Isn't that what the <langonly>it</langonly> tag in comps is for?

The implication was that this sort of backwards compatibility option would work even if the group didn't exist.

I've added langinstall, langremove, and langlist commands to yum-langpacks-0.3.0, and am pushing it to F-18 and F-17. Please let me know how this works for you.

yum-langpacks-0.3.0-1.fc17 has been submitted as an update for Fedora 17.
https://admin.fedoraproject.org/updates/yum-langpacks-0.3.0-1.fc17

Package yum-langpacks-0.3.0-1.fc17:
* should fix your issue,
* was pushed to the Fedora 17 testing repository,
* should be available at your local mirror within two days.
Update it with:
# su -c 'yum update --enablerepo=updates-testing yum-langpacks-0.3.0-1.fc17'
as soon as you are able to.
Please go to the following url:
https://admin.fedoraproject.org/updates/FEDORA-2012-11567/yum-langpacks-0.3.0-1.fc17
then log in and leave karma (feedback).

thanks for update, tested it.

$yum langinstall mr_IN 
doing expected thing, i.e install hunspell-mr and libreoffice-*-mr

but 
$yum groupinstall marathi-support

Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 319, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 185, in main
    (result, resultmsgs) = base.buildTransaction() 
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1140, in buildTransaction
    self.plugins.run('postresolve', rescode=rescode, restring=restring)
  File "/usr/lib/python2.7/site-packages/yum/plugins.py", line 187, in run
    func(conduitcls(self, self.base, conf, **kwargs))
  File "/usr/lib/yum-plugins/langpacks.py", line 303, in postresolve_hook
    add_matches_from_ts(conduit, group.langonly)
TypeError: add_matches_from_ts() takes exactly 3 arguments (2 given)

yum-langpacks-0.3.0-2.fc17 has been submitted as an update for Fedora 17.
https://admin.fedoraproject.org/updates/yum-langpacks-0.3.0-2.fc17

1) With the new update langinstall works fine. But, my question is will "yum grouplist" will continue to show "Marathi Support" as a available group to install? 

2)Also, following is expected results right? groupinstall is not working.

$sudo yum groupinstall "Marathi Support" 
Loaded plugins: langpacks, presto, refresh-packagekit
Package ibus-m17n-1.3.3-11.fc17.x86_64 already installed and latest version
Warning: Group marathi-support does not have any packages.
No packages in any requested group available to install or update

3) Why is it that "yum langinstall mr_IN" works without root access whereas yum groupinstall used to need root access?

yum-langpacks-0.3.0-2.fc17 has been pushed to the Fedora 17 stable repository.  If problems still persist, please make note of it in this bug report.

(In reply to comment #19)
> 1) With the new update langinstall works fine. But, my question is will "yum
> grouplist" will continue to show "Marathi Support" as a available group to
> install? 

The groups are likely to be removed soon - input methods merged into the input-methods group, and fonts into the font group.

> 2)Also, following is expected results right? groupinstall is not working.
> 
> $sudo yum groupinstall "Marathi Support" 
> Loaded plugins: langpacks, presto, refresh-packagekit
> Package ibus-m17n-1.3.3-11.fc17.x86_64 already installed and latest version
> Warning: Group marathi-support does not have any packages.
> No packages in any requested group available to install or update

That's expected if the ony things in the group are already installed.

> 3) Why is it that "yum langinstall mr_IN" works without root access whereas
> yum groupinstall used to need root access?

Because I forgot to add a permissions check. Oops.