This module give each user the ability to choose which language the admin interface is in.

The description on the module's project page sums this up: "The Translation Management Tool (TMGMT) module provides a tool set for translating content from different sources. The translation can be done by people or translation services of all kinds. It builds on and uses existing language tools and data structures in Drupal and can be used in automated workflow scenarios.

A distribution which is a central server for managing translation jobs.