Alternative approach to #243129.

From: damz <damz@damz-dev.local>


---
 common.inc |   57 +++++++++++++++++++++++++++++++++------------------------
 1 files changed, 33 insertions(+), 24 deletions(-)

diff --git includes/common.inc includes/common.inc
index dced29c..5e19ce3 100644
--- includes/common.inc
+++ includes/common.inc
@@ -1916,32 +1916,41 @@ function format_date($timestamp, $type = 'medium', $format = '', $timezone = NUL
   // Set the time zone for the DateTime object.
   date_timezone_set($date_time, $timezones[$timezone]);
 
-  for ($i = 0; $i < $max; $i++) {
-    $c = $format[$i];
-    if (strpos('AaeDlMT', $c) !== FALSE) {
-      $date .= t(date_format($date_time, $c), array(), array('langcode' => $langcode));
-    }
-    elseif ($c == 'F') {
-      // Special treatment for long month names: May is both an abbreviation
-      // and a full month name in English, but other languages have
-      // different abbreviations.
-      $date .= t(date_format($date_time, $c), array(), array('context' => 'Long month name', 'langcode' => $langcode));
-    }
-    elseif (strpos('BcdGgHhIijLmNnOoPSstUuWwYyZz', $c) !== FALSE) {
-      $date .= date_format($date_time, $c);
-    }
-    elseif ($c == 'r') {
-      $date .= format_date($timestamp, 'custom', 'D, d M Y H:i:s O', $timezone, $langcode);
-    }
-    elseif ($c == '\\') {
-      $date .= $format[++$i];
-    }
-    else {
-      $date .= $c;
-    }
+  // Pass the DateTime object and the langcode to the callback function.
+  _format_date_callback(array(), array('date_time' => $date_time, 'langcode' => $langcode));
+
+  return preg_replace_callback('/(\\\?)([AaeDlMTFBcdGgHhIijLmNnOoPSstUuWwYyZzr])/', '_format_date_callback', $format);
+}
+
+function _format_date_callback(array $matches, $options = NULL) {
+  static $date_time, $langcode;
+
+  if (isset($options)) {
+    $date_time = $options['date_time'];
+    $langcode = $options['langcode'];
+    return;
   }
 
-  return $date;
+  list(, $backslashes, $c) = $matches;
+
+  if (!empty($backslashes)) {
+    return $c;
+  }
+  elseif (strpos('AaeDlMT', $c) !== FALSE) {
+    return t(date_format($date_time, $c), array(), array('langcode' => $langcode));
+  }
+  elseif ($c == 'F') {
+    // Special treatment for long month names: May is both an abbreviation
+    // and a full month name in English, but other languages have
+    // different abbreviations.
+    return t(date_format($date_time, $c), array(), array('context' => 'Long month name', 'langcode' => $langcode));
+  }
+  elseif (strpos('BcdGgHhIijLmNnOoPSstUuWwYyZz', $c) !== FALSE) {
+    return date_format($date_time, $c);
+  }
+  elseif ($c == 'r') {
+    return format_date($timestamp, 'custom', 'D, d M Y H:i:s O', $timezone, $langcode);
+  }
 }
 
 /**