added missing language string already present in default theme

Author: cfoe

interface/web/domain/lib/lang/de_domain_list.lng

@@ -2,4 +2,5 @@
 $wb['list_head_txt'] = 'Domains';
 $wb['add_new_record_txt'] = 'Neue Domain hinzufügen';
 $wb['domain_txt'] = 'Domain';
+$wb['user_txt'] = 'Kunde';
 ?>

interface/web/domain/lib/lang/en_domain_list.lng

@@ -2,4 +2,5 @@
 $wb['list_head_txt'] = 'Domains';
 $wb['add_new_record_txt'] = 'Add new Domain';
 $wb['domain_txt'] = 'Domain';
+$wb['user_txt'] = 'Client';
 ?>