Confluence ships with a number of bundled language packs. These languages appear as options on the 'Language Configuration' screen in the Administration Console when choosing a default language and as 'Language' options for users in their user settings. You can make additional languages available for selection by installing language packs. Please note, you must be a Confluence administrator to install a language pack.
Language packs are plugins. The process of installing a language pack is the same as installing a new plugin.
Installing a Language Pack using the Universal Plugin Manager
Universal Plugin Manager を使用して言語パックをインストールする手順