You have to put it into zp-core/locale and then you can switch the language for the backend on the options. There is also a selector to switch the language on the frontend (theme). If that is there depends on if the plugin for that is enabled and the theme used has support for that. Norwegian is severely outdated btw.
If you want to use your site in multilingual mode you have also to enable that on the options. The you can fill in content like titles or descriptions for each language separately. You may want to remove languages from the locale folder you don't need.