1) make sure you have v2.16beta6 or later of routers2.cgi
2) download the latest Language Pack from the website
3) install the appropriate language files -- the lang_xx.conf files into the same location as your routers2.conf (although you can override this with the langdir setting in the routers2.conf), and the xx/ icon directories as subdirectories of your rrdicons directory (you can change this by modifying the iconurl definition in the lang_xx.conf files)
4) in your routers2.conf, add 'language = xx' to the [routers.cgi] section for default, or to individual people's [user-yyyy] sections.
When you go to the 'personal preferences' page of routers2.cgi, you should see a language selector. You can test your new languages here, as well.
In the above example, xx is your language code, which may be more than 2 characters. So far, we have French, German, Russian, and Chinese Traditional (although the icons are not ready yet for Chinese).
I'm hoping to have some instructions and even install scripts ready for the language pack when 2.16 is officially released.
UNIX Systems, ITSS, University of Auckland, NZ
Woe unto them that rise up early in the morning... -- Isaiah 5:11