Some additional information/documentation is at
http://translatewiki.net/wiki/Page_translation . An overview of
translatewiki's translatable pages is at
http://translatewiki.net/wiki/Special:PageTranslation
The translatable pages can also be exported as gettext file for offline
translation, and the translated gettext files can be uploaded again through
http://translatewiki.net/wiki/Special:ImportTranslations ('translate-import'
access right needed).
Like annew says, there probably are quirks, because the feature hasn't been
used on a large scale; mainly because no production wikis that have a
significant volume of translatable pages are using it yet. Help on further
development is appreciated. Translatewiki.net's purpose is getting user
interfaces translated, so we only use it for our most basic documentation for
translators; we'd rather have them translate UIs than documentation of the
wiki itself.
Siebrand