You can configure a Drupal website to use a language other than English and you can configure a site to use multiple languages.
If your site uses only one language, you can install a distribution which allows you to select the interface from more than 80 available languages. For more information, see the Localized Drupal Distribution project page.
If your site requires the interface to be displayed in multiple languages or if you need to customize the interface of a single language site, the first step is to enable the multilingual capabilities of Drupal.
You can also configure a Drupal site to allow your users to switch languages and you can translate content into multiple languages.
For information about writing code for localized modules, see the Localization API and the Multilingual support section of the Develop for Drupal guide.
The following resources are also helpful when building multilingual sites: