Several modules exist that extend the multilingual capabilities of your site. Apart from the modules documented here, you can browse the multilingual section of the modules list to see all projects, sorted by popularity. You may want to additionally filter by version to see, for example, only modules compatible for the latest Drupal version.
Of these modules, you should at least install the Internationalization package of modules which provides several important features not currently built into Drupal core, and Localization update which automatically fetches updated translations of strings hardcoded in all the core and contributed modules you have installed on your site.
Below, you can find a list of modules that have their own documentation pages.