I edited administrator/components/com_languages/actions/save.action.php on line 78,It need not to check and create $dir/$lang.po when install language.But when you new language it proper create $dir/$domain.po from $untranslated/$domain.pot.And I edited line 125 follow Andphe suggest me.Not only that,I edited file administrator/components/com_languages/views/templates/langform.tpl.php to cannot save if _ISO value not same $language->charset value.