From Gallery Codex

Internationalization of Gallery 2

Gallery 2 is completely internationalized and it ships with translations into various languages (complete list of the existing translations).

Requirements

To use Gallery 2 in another language than English, your webserver / environment must meet some requirements:

• PHP: The gettext extension must be installed and loaded
• Operating System: All locales (languages) that you would like to use must be supported by the operating system of the server

Overview

• Language Settings: Overview over the language settings in Gallery 2
• MultiLanguage Module: An optional module to also manually translate your own content
• Relevant FAQ entries:
  • I changed the language but nothing happens. What's wrong?
  • Where I should see dates I see "Wrong charset, cannot convert" or "Illegal character encoding" or "Illegal recode request".. what is wrong?
• Localization: Instructions for translators