It provides a generic translation database backend with a community localization user interface, which allows people to collaborate on translating projects to different languages. It currently contains tools to translate Drupal projects as well as general Gettext based sources.
Read Using Drupal as a collaborative software translation tool for setup instructions.
You'll need jQuery Update 2.x (which includes jQuery 1.3.x) to make the UI work properly. Sorry, version information is not possible to specify in .info files on Drupal 6, so we can only document this requirement. The Plural formula configurator is also required.
This module suite is used on localize.drupal.org to facilitate community translation. Check out the documentation pages on How to contribute on the translation server if you are interested in helping out with translations.
The use of Localized Drupal to install your Drupal site right away is suggested. This install profile sets up your Drupal site with localizations from drupal.org's server downloaded on the fly.
For sites already set up, the Localization update module is highly recommended. This helps you keep updated with the localization server's translations on your site even if you update modules.
Finally, the Localization client module is great to fine-tune your translations and even contribute back to the community in the process.