fixes undefined index error

plugins/LanguagesManager/TranslationWriter/Filter/EncodedEntities.php

@@ -37,7 +37,8 @@ class EncodedEntities extends FilterAbstract
         foreach ($translations as $pluginName => $pluginTranslations) {
             foreach ($pluginTranslations as $key => $translation) {
 
-                if ($this->baseTranslations[$pluginName][$key] != Translate::clean($this->baseTranslations[$pluginName][$key])) {
+                if (isset($this->baseTranslations[$pluginName][$key]) &&
+                    $this->baseTranslations[$pluginName][$key] != Translate::clean($this->baseTranslations[$pluginName][$key])) {
                     continue; // skip if base translation already contains encoded entities
                 }