In a default installation of Cotonti, all text is displayed in English. This is common known, but not always suitable for your site.
Those texts can be change via the language files.
There are already localization available for Cotonti. See http://www.cotonti.com/locales/.
Versions of core language files can slighly differ from version to version, so be sure to download proper one. If you can not find your version just try to download file for previous version or use special service to localize...