2012-05-01: Support was added for Waymarked Trails. (Other news...)
Potlatch 2
Fragment of a discussion from Translating talk:OpenStreetMap
We have not been contacted about this for any developer types. From what I have seen, the i18n is through compiled flash files. We do not support that. I would advise you to inform with the OSM developer community.
Not exactly true, we have had little contact, but last time it(i18n) was nowhere near ready yet.
Nike
It is possible to translate the most visible messages using .properties files. I’ve gotten those messages translated into Vietnamese by filing ticket 3746 in OpenStreetMap Trac. The l10n files all live in git.
Minh Nguyễn (talk, contribs)