...actually, by taking the last package you still would have to use some modification in config/main.inc.php to set it from "en" to "de" if you prefer german...and, because these are missing, localization/index.inc shouldlook like this:
$Id: index.inc 323 2006-08-23 21:36:37Z thomasb $
$rcube_languages = array(
'de_DE' => 'Deutsch (DE)',
'en_US' => 'English (US)'
$rcube_language_aliases = array(
'de' => 'de_DE',
'en' => 'en_US'
$rcube_charsets = array();
Well and finally the de_DE package (...korrigiert und erweitert) would be in the attachment :-)
...hm, then, at last you might have to take a look in the default-skin-buttons-folder, if all png's an the gif-file are ok, three of mine where broken, so I took them from one of the other, similar skins