4 - Multilingual for developers
Writing code for multilingual sites
Keep in mind that Drupal's default language is english. It doesn't matter what is your site default language, all code you write must be in english to avoid problems. This is true even if your site has only one language (other than english). You should write all your code in english (using the t() function to make strings translatable) and translate it using the drupal interface. Drupal will always consider that whatever is in code is english.
Views + Features bug (modules)
When exporting a Views using Features you might see that translations may get lost. Actually, if you edit your Views, add a space to the end of the title and save it, the translations get back to where they belong. This is one of the few annoying bugs that can make you cry if you are not aware of.