Drupal's locale module is a monster! It does lots of things to enable language support, including the following:
- Configure/maintain a list of languages supported on the site
- Configure the selection method for these languages, provide language switcher UIs
- Translate the Drupal software to the configured languages
- Provide language assignment user interface to path module and node module
- Provide translatable date formats
- Import and export Gettext translation files for UI translation
- Provide database space for configuration translation (UI implemented in contributed i18n.module)
- Provide hooks for entity field translation (UI implemented in contributed entity_translation.module)
The principal goal of the multilingual initiative for Drupal 8 is to spread language support wider, so more and more modules will have language support built-in. The path module language UI already got moved to path module (see http://drupal.org/node/1236680), and node is on its way (see http://drupal.org/node/540294). Also, Drupal 8 does not support use of locale module for configuration translation anymore (see http://drupal.org/node/1188430).
However, locale module still does too much! Not all of its features belong to other existing modules, and to support various foreign language and multilanguage models, we need to break locale module down to smaller pieces to make sense for users. To figure this out, I've opened an issue at http://drupal.org/node/1293304 and included some fancy overview graphs for us to help focus the conversation and figure out which piece makes sense at which area of the Drupal codebase. Your feedback would be very welcome on the issue (comments turned off here)!