Welcome to Drupal project translations! This service is used by translators from around the world to maintain localizations of all projects on drupal.org. Just pick your language and you'll be able to download existing work and contribute to the translations.
Install Drupal localized with translations from here using Localized Drupal. You can also set it up to contribute to these translations right from your Drupal site! For already installed sites, use the Localization update module to download the right translation files for the right projects you use.
Drupal core is just one of the 15790 projects translated on this server. Check them out.