You will first have to add the portal language in the Language Manager section of the backend administration panel, but since you already visited the Portal Localization section I assume that you already did that.
Portal localization section takes care of resources (.resx files or database settings if you are using database provider). These are used for button and label captions and similar small-size localization settings that are more or less "static", and set by programmers when they are designing the user interface. MonoX uses standard ASP.NET localization concepts here (and adds the provider-based architecture on top of that).
Navigation menus, HTML texts, list items, poll options, and other "dynamic" content is not managed via resources. Each of these features has its own management utility (HTML editor allows you to edit the content in place, most of other parts has their management counterpart in the administraion section). [b]Navigation is managed in the "Pages" section of the admin section: the treeview on the left side allows you to manipulate the navigation hierarchy.[/b] Just change the active language in the dropdown box at the top of the screen and you are ready to go. You can add pages to navigation by clicking on the ckeckboxes next to the page names, but navigation item do not have to share a name with the page they are pointing to. You can have different types of navigation items (containers and external links that are also used in URL rewriting scenarios).
Let me know if you need additional help.