Here are some resources about Joomla language packs:
- Download existing Joomla language packs at "Translations for Joomla":
http://extensions.joomla.org/extensions/languages/translations-for-joomla
- How to add a language pack to your Joomla installation:
http://www.siteground.com/tutorials/joomla/joomla_language.htm
- How to create a new language pack for Joomla - from the documentation:
http://docs.joomla.org/How_to_create_a_language_pack
- How to create a new language pack for Joomla - forum:
http://forum.joomla.org/viewtopic.php?f=485&t=276068&start=0&st=0&sk=t&sd=a