Setting up a basic Drupal website in English is relatively easy. Setting up a multilingual website isn't as obvious as you would hope it to be. Knowing a thing or two about how and where to find help on drupal.org is a must. See References for more information.
The present article does not address the topic of multilingual menus.
Alright, let's do it.
admin/config/regional/language) and add a new language to the list. In this article, I'll be adding French.
admin/config/regional/language/edit/en). In the current example, I've added "en" for English and "fr" for French. Note the warning: Modifying this value may break existing [node] URLs. I had created a couple of nodes prior to making this change and encountered many nagging problems related to bad links. Deleting and recreating all existing nodes solved all those problems. If you have many existing nodes, export them before deleting them. Then import them back. You can do this more easily with the Node export module (http://drupal.org/project/node_export). Also, make sure the option "Determine the language from the URL (Path prefix or domain)" is enabled at
admin/config/regional/translateand click on the Import tab. Import the translation package you've just downloaded into the desired language (drupal-7.x.fr.po into French for this article). You may need to import other project (module) packages (e.g. Views, Panels, etc.). But you can do that later.
admin/structure/block. Look for Language switcher and set the region (sidebar first in the present case). Click the Save blocks button at the bottom of the page. Goto your Home page and check that the block is showing. Clicking the different languages will switch the interface back and forth between them.
admin/structure/types/manage/articleand click on the Publishing options tab (the horizontal ones) and activate the Enabled, with translation radio button. Then click the Save content type button. Repeat for all content type that need a language specific translation.
That's it. Your website is multilingual ready. Now every time you create a new node (Article, Page, etc.), you'll have to specify which language it belongs to. Language neutral nodes will be displayed just the same for all languages. That's why this article appears in English as well as in French. Check it out.
p.s. I'm thinking screen captures would be nice, right? I'm also thinking about a screencast version. That would be cool...