The language fallback logic has been moved onto the language manager

The language_fallback_get_candidates() function has been moved onto the language manager and now accepts a $context parameter describing the context where fallback is applied:

<?php
public function getFallbackCandidates($langcode = NULL, array $context = array());
?>

The $context parameter is an associative array of arbitrary data that can be useful to determine the fallback sequence. The following keys are used in core:

• langcode: The context language.
• operation: The name of the operation indicating the context where language fallback is being applied, e.g. 'entity_view'.
• data: An arbitrary data structure that makes sense in the specified context, e.g. an entity.

Also hook_language_fallback_candidates_alter() now receives the $context parameter, and an operation-specific version of the hook is available if the operation key is defined:

<?php
/**
 * Implements hook_language_fallback_candidates_OPERATION_alter().
 */
function foo_language_fallback_candidates_entity_view_alter(array &$candidates, array $context) {
  // We know that the current OPERATION deals with entities so no need to check
  // here.
  if (!empty($context['data']) && $context['data']->entityType() == 'node') {
    $candidates = array_reverse($candidates);
  }
}
?>