Every page can have a translation in any language, though initially each page will be written in a single language. Each user records which languages they can read, and their relative fluency; when a user visits a page, they see the translation they can read most fluently.
A translation can be "in sync", "not in sync", "not in sync, older" and "not in sync, newer", with another translation. If two translations are "in sync" and one is edited, that translation becomes "not in sync, newer", and the other one "not in sync, older". If the other one is then also edited (not translated), the status of both will change to just "not in sync".
If, when a user visits a page, a translation is "not in sync" (or "not in sync, older/newer") with the translation into another language spoken by the visitor, or such a translation is missing for one of the languages spoken by the visitor, the visitor will be presented an option to translate and synchronize the texts. If they choose to do so, they are presented with a two-pane editor with the text in both languages.
When they save, the texts are considered in sync. If both translations were edited, all other translations will become "not in sync" with these two. Otherwise, the changed translation will be "in sync" with all the one that are "in sync" with the unchanged translation.
One might choose to get one of the most up-to-date translations, rather than a translation in a language they are more fluent with. One might also want some type of notification that a translation is "not in sync" or "not in sync, older" with respect to a language one does not understand.
Note that each page translation also has a WikiName, and WikiWords are looked up in the set of WikiNames for the language of the translation they are found in. Optionally, a specific language can be defined within the link, allowing links to as-yet untranslated pages.
(-- Originally anon, contact at email@example.com; has since been rewritten)
This system could also be used to provide (and synchronize) audio recordings of people reading out pages, simplified presentations for newcomers, and other presentational formats - perhaps of interest for accessibility reasons, and certainly an intriguing idea. It also seems applicable to DigestedChanges, if it can be stretched to synchronizing a page with a set of pages. -- ChrisPurcell