The interface language in umbraco can be extended by editing small xml files and placing them in the /umbraco/config/lang folder.
The following languages can be downloaded from http://old.umbraco.org/frontpage/download/languagepacks.aspx (besides the default english language)
- German - Translated by Christian Langreiter
- Italian - Translated by Stevie B. Gibson
- Spanish - Translated by Gustavo Martinez
- Dutch - Translated by Boris Leenaars
- Danish - Translated by Niels Hartvig / umbraco
- Swedish - Translated by Toft Stade
- Portuguese/Brazil - Translated by George Justo / KnowledgeCenter
- Norwegian - Translated by Thøger Amundsen / Doorway Consulting
There are also alternate language packs that have been translated or modified by Umbraco users.