OpenStreetMap (homepage) is a free editable map of the whole world. It is made by people like you (released under the Creative Commons Attribution Share Alike 2.0 license).
It is possible to translate the OpenStreetMap website and the Potlatch 2 editor at translatewiki.net. User Siebrand coordinates the localisation. Changes to messages on translatewiki.net are usually exported within 2 weeks. The OSM website is updated every few weeks, as far as we know. More parts of OpenStreetMap may be added later; for now, see the OpenStreetMap Wiki for details. Note that the actual map data must be translated using an OpenStreetMap editor, such as Potlatch 2 or JOSM (details and instructions). The JOSM editor startup page can be translated on its website, and the editor itself in Launchpad.
OSM uses rails-i18n, based on CLDR data, to generate plural forms. The plural software keys for each language on rails-i18n, are here. See Unicode CLDR page for an explanation of the plural keys for translators. Advice on writing plural syntax for CLDR data is given here.
Software help, including a glossary of terms, is available on the OpenStreetMap Wiki.
- trunk (Languages with a translation percentage above 35% are committed to version control)