FusionForge uses standard GNU gettext for its internationalisation system. This system is widely known amongst the i18n community, which removes the burden of having to learn a home-made translsation system.
The Debian i18n people are kindly hosting the FusionForge translation effort on their Pootle instance, and the results are regularly merged into the development code.
As of end of March, 2009, there are a handful of languages with rather good translation status: French is more than 90% translated, Russian is above 80%, German is above 60%, and Spanish, Catalan, traditional Chinese and simplified Chinese are all above 50%. Other languages with a reasonably good status include Basque, Italian, Brazilian Portuguese, Korean, Dutch and Swedish (all above 30%). These numbers should be taken with a grain of salt (the untranslated strings are often the ones least frequently seen), though.
Potential translators are encouraged to create an account on the Pootle server and start to get a feel on how it works. It's designed to be usable by a wide range of users, from the occasional user who just wants to offer a suggestion for one string to the seasoned translator who can juggle *.po files blindfolded.