Issue#3975: [UX] Installer: Revamp the language selection page

backdrop/backdrop-issues#3975

core/includes/install.core.inc

@@ -1438,16 +1438,38 @@ function install_select_language_form($form, &$form_state, $files) {
   );
 
   if (count($files) == 1) {
-    $form['help'] = array(
+    $directory = settings_get('locale_translate_file_directory', conf_path() . '/files/translations');
+
+    $steps = array();
+    $steps[] = st('Download translation files from the <a href="https://localize.backdropcms.org/translate/languages" target="_blank">translation server</a>.');
+    $steps[] = st('Place the downloaded <code>.po</code> files into the following directory: <pre>@dir</pre>', array('@dir' => $directory));
+    $steps[] = st('<a href="@reload_link">Reload this page</a>. The languages added in the previous step should now have become available in the select menu above.', array('@reload_link' => check_url(backdrop_current_script_url())));
+
+    $more_info = st('For more information on installing Backdrop in different languages, visit the <a href="https://backdropcms.org/installing-in-other-languages" target="_blank">Backdrop user guide page</a>.');
+
+    $markup = st('Follow these steps to enable other languages for the Backdrop installer:');
+    $markup = '<p>' . $markup . '</p>';
+    $markup .= theme('item_list', array('items' => $steps, 'type' => 'ol'));
+    $markup .= '<p>' . $more_info . '</p>';
+
+    $form['languages_help'] = array(
+      '#type' => 'fieldset',
+      '#title' =>  st('Install in another language'),
+      '#collapsible' => TRUE,
+      '#collapsed' => TRUE,
+    );
+    $form['languages_help']['help'] = array(
       '#type' => 'help',
-      '#markup' => '<a href="' . check_url(backdrop_current_script_url(array('translate' => 'true'))) . '">' . st('Learn how to install Backdrop in other languages') . '</a>',
+      '#markup' => $markup,
     );
   }
+
   $form['actions'] = array('#type' => 'actions');
   $form['actions']['submit'] =  array(
     '#type' => 'submit',
     '#value' => st('Save and continue'),
   );
+
   return $form;
 }