Undefined index: es_es 012-ps-multi-languages\ps-multi-languages.php on line 89

I have wordpress in Spanish with

define (‘WPLANG’, ‘es_ES’), in wp-config.php

How I can make the plugin work?

In config add:

$this->multilingual = array(
							'en' => 'English',
							'zh' => 'Chinese',
							'ja' => 'Japanese',
							'fr' => 'French',
							'es' => 'Espa?ol',

	);

	$this->multilingual_code = array(
							'en' => 'en_US',
							'zh' => 'zh_CN',
							'ja' => 'ja',
							'fr' => 'fr_FR',
							'es' => 'es_ES',
	);

	$this->search_multilingual_title = array(
							'en' => 'Search Results For',
							'zh' => '查询结果',
							'ja' => '検索結果',
							'fr' => 'Résultats de la recherche',
							'es' => 'Resultados',
	);

define( 'MULTILINGUAL_WPLANG' , 'es' );

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https://www.ads-software.com/extend/plugins/012-ps-multi-languages/