[BUGFIX] Fix language filter in mail queue

Classes/Domain/Repository/MailRepository.php

@@ -89,7 +89,10 @@ class MailRepository extends AbstractRepository {
 			$constraintsAnd[] = $query->equals('template_name', $filters['filterTemplate']);
 		}
 
-		$constraintsAnd[] = $query->equals('sys_language_uid', (int) $filters['filterLanguage']);
+		if ($filters['filterLanguage']) {
+			$constraintsAnd[] = $query->equals('sys_language_uid', (int) $filters['filterLanguage']);
+		}
+
 		$constraintsOr = [];
 		if ($filters['filterSearch']) {
 			$search = '%' . $filters['filterSearch'] . '%';

Resources/Private/Partials/Queue/Filter.html

@@ -34,6 +34,7 @@
 							   multiple="0"
 							   size="1"
 							   property="filterLanguage"
+							   prependOptionLabel="{f:translate(key:'LLL:EXT:core/Resources/Private/Language/locallang_general.xlf:LGL.allLanguages')}"
 							   optionValueField="languageId"
 							   optionLabelField="title"
 							   options="{languages}"