Translations:Help:Extension:Translate/Configuration/23/en

Provided that the closing &lt;/translate> tag exists, the source page is too big. This starts happening with some translations if the source page size is near 50 kilobytes. Make the page shorter or increase pcre.backtrack_limit by setting  ini_set( 'pcre.backtrack_limit', 400000 ); in LocalSettings.php or  pcre.backtrack_limit=400000  in your PHP configuration (php.ini).