diff --git a/core/modules/file/file.field.inc b/core/modules/file/file.field.inc
index 3305a00..f42a15c 100644
--- a/core/modules/file/file.field.inc
+++ b/core/modules/file/file.field.inc
@@ -722,7 +722,15 @@ function theme_file_widget_multiple($variables) {
  *
  * @ingroup themeable
  */
-function theme_file_upload_help($variables) {
+function file_upload_help($variables = array()) {
+  // Merge in defaults.
+  $variables += array(
+    'description' => '',
+    'upload_validators' => array(),
+    'cardinality' => NULL,
+    'separator' => '<br />',
+  );
+
   $description = $variables['description'];
   $upload_validators = $variables['upload_validators'];
   $cardinality = $variables['cardinality'];
@@ -730,40 +738,43 @@ function theme_file_upload_help($variables) {
   $descriptions = array();
 
   if (strlen($description)) {
-    $descriptions[] = _filter_htmlcorrector($description);
+    $descriptions['description'] = _filter_htmlcorrector($description);
   }
   if (isset($upload_validators['file_validate_size'])) {
-    $descriptions[] = t('Files must be less than !size.', array('!size' => '<strong>' . format_size($upload_validators['file_validate_size'][0]) . '</strong>'));
+    $descriptions['file_validate_size'] = t('Files must be less than !size.', array('!size' => '<strong>' . format_size($upload_validators['file_validate_size'][0]) . '</strong>'));
   }
   if (isset($upload_validators['file_validate_extensions'])) {
-    $descriptions[] = t('Allowed file types: !extensions.', array('!extensions' => '<strong>' . check_plain($upload_validators['file_validate_extensions'][0]) . '</strong>'));
+    $descriptions['file_validate_extensions'] = t('Allowed file types: !extensions.', array('!extensions' => '<strong>' . check_plain($upload_validators['file_validate_extensions'][0]) . '</strong>'));
   }
   if (isset($cardinality)) {
     if ($cardinality == -1) {
-      $descriptions[] = t('Unlimited number of files can be uploaded to this field.');
+      $descriptions['cardinality'] = t('Unlimited number of files can be uploaded to this field.');
     }
     else {
-      $descriptions[] = format_plural($cardinality, 'This field can store only one file.', 'This field can store at most @count files.');
+      $descriptions['cardinality'] = format_plural($cardinality, 'This field can store only one file.', 'This field can store at most @count files.');
     }
   }
   if (isset($upload_validators['file_validate_image_resolution'])) {
     $max = $upload_validators['file_validate_image_resolution'][0];
     $min = $upload_validators['file_validate_image_resolution'][1];
     if ($min && $max && $min == $max) {
-      $descriptions[] = t('Images must be exactly !size pixels.', array('!size' => '<strong>' . $max . '</strong>'));
+      $descriptions['file_validate_image_resolution'] = t('Images must be exactly !size pixels.', array('!size' => '<strong>' . $max . '</strong>'));
     }
     elseif ($min && $max) {
-      $descriptions[] = t('Images must be between !min and !max pixels.', array('!min' => '<strong>' . $min . '</strong>', '!max' => '<strong>' . $max . '</strong>'));
+      $descriptions['file_validate_image_resolution'] = t('Images must be between !min and !max pixels.', array('!min' => '<strong>' . $min . '</strong>', '!max' => '<strong>' . $max . '</strong>'));
     }
     elseif ($min) {
-      $descriptions[] = t('Images must be larger than !min pixels.', array('!min' => '<strong>' . $min . '</strong>'));
+      $descriptions['file_validate_image_resolution'] = t('Images must be larger than !min pixels.', array('!min' => '<strong>' . $min . '</strong>'));
     }
     elseif ($max) {
-      $descriptions[] = t('Images must be smaller than !max pixels.', array('!max' => '<strong>' . $max . '</strong>'));
+      $descriptions['file_validate_image_resolution'] = t('Images must be smaller than !max pixels.', array('!max' => '<strong>' . $max . '</strong>'));
     }
   }
 
-  return implode('<br />', $descriptions);
+  // Allow other modules to modify the
+  Drupal::moduleHandler()->alter(__FUNCTION__, $descriptions, $variables);
+
+  return implode($variables['separator'], $descriptions);
 }
 
 /**
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 0d66adb..1e5de89 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -596,9 +596,6 @@ function file_theme() {
     'file_formatter_table' => array(
       'variables' => array('items' => NULL),
     ),
-    'file_upload_help' => array(
-      'variables' => array('description' => NULL, 'upload_validators' => NULL, 'cardinality' => NULL),
-    ),
   );
 }
 
diff --git a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
index 63564fa..1cbca0e 100644
--- a/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
+++ b/core/modules/file/lib/Drupal/file/Plugin/field/widget/FileWidget.php
@@ -164,7 +164,7 @@ protected function formMultipleElements(EntityInterface $entity, array $items, $
       // field. These are added here so that they may be referenced easily
       // through a hook_form_alter().
       $elements['#file_upload_title'] = t('Add a new file');
-      $elements['#file_upload_description'] = theme('file_upload_help', array('description' => '', 'upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
+      $elements['#file_upload_description'] = file_upload_help(array('description' => '', 'upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
     }
 
     return $elements;
@@ -225,7 +225,7 @@ public function formElement(array $items, $delta, array $element, $langcode, arr
 
     $default_fids = $element['#extended'] ? $element['#default_value']['fids'] : $element['#default_value'];
     if (empty($default_fids)) {
-      $element['#description'] = theme('file_upload_help', array('description' => $element['#description'], 'upload_validators' => $element['#upload_validators'], 'cardinality' => $cardinality));
+      $element['#description'] = file_upload_help(array('description' => $element['#description'], 'upload_validators' => $element['#upload_validators'], 'cardinality' => $cardinality));
       $element['#multiple'] = $cardinality != 1 ? TRUE : FALSE;
       if ($cardinality != 1 && $cardinality != -1) {
         $element['#element_validate'] = array('file_field_widget_multiple_count_validate');
diff --git a/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php b/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
index d0ae8fa..9f3af40 100644
--- a/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
+++ b/core/modules/image/lib/Drupal/image/Plugin/field/widget/ImageWidget.php
@@ -87,11 +87,11 @@ protected function formMultipleElements(EntityInterface $entity, array $items, $
     if ($cardinality == 1) {
       // If there's only one field, return it as delta 0.
       if (empty($elements[0]['#default_value']['fids'])) {
-        $elements[0]['#description'] = theme('file_upload_help', array('description' => $this->fieldDefinition->getFieldDescription(), 'upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
+        $elements[0]['#description'] = file_upload_help(array('description' => $this->fieldDefinition->getFieldDescription(), 'upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
       }
     }
     else {
-      $elements['#file_upload_description'] = theme('file_upload_help', array('upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
+      $elements['#file_upload_description'] = file_upload_help(array('upload_validators' => $elements[0]['#upload_validators'], 'cardinality' => $cardinality));
     }
 
     return $elements;
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 8a15656..fe8ab8b 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -54,7 +54,7 @@ function locale_translate_import_form($form, &$form_state) {
   $form['file'] = array(
     '#type' => 'file',
     '#title' => t('Translation file'),
-    '#description' => theme('file_upload_help', array('description' => t('A Gettext Portable Object file.'), 'upload_validators' => $validators)),
+    '#description' => file_upload_help(array('description' => t('A Gettext Portable Object file.'), 'upload_validators' => $validators)),
     '#size' => 50,
     '#upload_validators' => $validators,
     '#attributes' => array('class' => array('file-import-input')),