I know this thread is ancient now but after reading the instructions
(current as of this writing) on the language pack page, which says to look under the SYSTEM menu in the ACP, I was confused.
Posting this in case it may help someone else, until the instructions are corrected at the link above. The language packs are now managed and installed under the CUSTOMIZE menu in the ACP. There is a "LANGUAGE MANAGEMENT" heading with a link under that to allow you to install and delete language packs.