To download it, follow the link: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=646e311a-aaf3-4d30-b03c-2f3c70d19a22
Installation is really easy. The only point that can cause some trouble is the correct language pack download. Most of SharePoint administrators have already download English Language pack instead of expected file. Indexes in Google or Bing contains information in different languages. This content is related to the same url. But depending on your regional settings, page will certainly be displayed in English. That’s why a query using French terms will bring us to a English Language Pack download page and we install English Language Pack on a SharePoint in English. So be sure to select the correct language as shown on the following screenshot:
Note that most usual Language Packs use between 110 and 170MB. Here is a sample with French L.P. (We can show that filename that is send by download server is not really explicit):
After this, you know what to do… next, next et next :-)
As indicated, be sure to run the configuration wizard as soon as you have the possibility!
After this, go to the site settings of a SharePoint site. You’ll see a Language settings.

By clicking on the link, you will have the possibility to select available languages for your site:
Users will be able to select the display language they prefer…
Everything that is "out-of-the-box" is translated (menus, ribbon, …)
There is a lot of other features about multilinguism. I will certainly publish some other posts about it in the next few weeks.