That is what the Security -> Web Users and Security -> Web Permissions (in the MODx Manager) is for.
With Web Permissions, you will need to create two Web User Groups in the Web User Groups tab, then create two corresponding Resource Groups in the Resource Groups tab, then connect each Web User Group to its corresponding Resource Group in the User/Resource Group Links tab.
Next, when creating the documents that you want Web User Group #1 to view, assign it to Resource Group #1, and those documents that are for Web User Group #2 get assigned to Resource Group #2.
Now, when a Web user is created, assign him to Web User Group #1 or Web User Group #2, and when he logs in he’ll be able to see those pages. Wayfinder will use the groups (checking the logged-in user’s
SESSION values ) to show or not show the pages in the menu. Anyone not logged in to the proper group who tries to directly access the page will get sent to your "Unauthorized Page", which is determined by the Unauthorized page setting in Tools -> Configuration, the Site tab. You can create a special page just for this, perhaps with a login form, and put that document’s ID in the Unauthorized page field, or leave it at the default "1", which is your home page.
There are a number of ways to deal with multilanguage support;
http://wiki.modxcms.com/index.php/Make_Multi_Lingual_Site is a relatively simple way, and
http://svn.modxcms.com/docs/display/ADDON/YAMS is a more complex complete solution.