Multilingual Setup Checklist
The easiest way to setup Drupal's multilingual system is using the Status Check of Translation Management.
Both experienced and beginner Drupal developers find the multilingual system complex and tricky. This page summarizes everything and highlights incorrectly configured items.
Go to Administer » Content management » Translation Management » Status Check
This page checks that i18n is installed and that its modules are enabled.
It also goes through all the content types in the site and checks that multilingual support is enabled for them and that the different fields are configured as translatable.
It says that the Revisit after field is not translatable. Whether we want to translate this field or not is up to us. To configure this field as translatable, we click on the page edit link in the warning. Each warning will include a link to fix the problem.
This link takes us to the Page setup. There, we can scroll to Content Translation and choose this field for translation.