We welcome translations to new languages, or improvements to the currently available languages. Send translations to the mailing list, or attach them to an issue in Jira. Make sure you use UTF-8 encoding in your files (except for the .properties files -- see below). Also, check on the mailing list if anybody else is working on the same language as you.
Daisy and the Daisy Wiki can be translated to different languages. For this purpose, text to be displayed to users is retrieved from a language-specific file, usually called a resource bundle.