CiviCRM can be configured to be used in another language than US English, for example:
- the interface can be set to another language,
- the configurations can be adapted to a specific region (date formats, number formats, currency),
- some of the data can be in multiple languages (known as "multi-lingual installs"), such as a contribution or event page that has a title and introduction in multiple languages (so that you can have a single contribution objective, or a single list of participant for a same event).
The biggest challenge is probably translating the user interface of CiviCRM, which has many strings (text), CiviCRM being a big project with a few components (civimail, civievent, etc). The most active and complete translations at the moment are Spanish, Dutch, Hungarian, Danish, French, Norwegian, Chinese/Mandarin (China mainland and Taiwan), Japanese, Russian, German and Swedish.
How to get started?
* The main translation/i18n documentation is on the wiki: http://wiki.civicrm.org/confluence/pages/viewpage.action?pageId=88408149
* Join a translation team on Transifex, where the translations are managed: https://www.transifex.com/projects/p/civicrm/
(and please read/create/update the translation glossary on the wiki, http://wiki.civicrm.org/confluence/display/CRMDOC/Resources+for+Translators
* Read the recent blog posts about internationalisation and localisation: https://civicrm.org/category/civicrm-blog-categories/internationalization-and-localization
There are often talks related to translation at CiviCons. Hopefully the video of the CiviCon London 2013 presentation should soon be available. In the mean time, you can consult the slides: http://london2013.civicrm.org/sessions/parlez-vous-civicrm-internationalisation-and-so-many-other-languages
And of course, please feel free to ask questions and participate to discussions on this forum!
Developers interested in i18n might want to subscribe to the civicrm-intl mailing list: http://lists.civicrm.org/lists/info/civicrm-intl