A language pack is a mechanism used by some Autodesk products to provide another language for the user interface and the documentation. You can now install additional standalone language packs, and switch between languages without having to uninstall and reinstall.
Language switching functionality is now supported for:
When you launch Autodesk Inventor or Autodesk Inventor LT by a language-specific Start menu shortcut, that language becomes the current language for Inventor.
Download language packs from http://www.autodesk.com/inventor-languagepacks.
For more information refer to the topics in the Installation section: http://autodesk.com/wikihelp-pds-install-2013-enu