Upon further reflection, I have decided to give the language_id a try.
Salvo (or anyone else willing to give it a try), please try these sql statements:
if (isset($HTTP_GET_VARS['description'])) {
$search_query = tep_db_query("select ad.articles_name, a.articles_id, ad.articles_description from " . TABLE_ARTICLES_DESCRIPTION . " ad inner join " . TABLE_ARTICLES . " a on ad.articles_id = a.articles_id where a.articles_status = '1' and ad.language_id = '" . (int)$languages_id . "' and (ad.articles_name like '%" . $keywords . "%' or ad.articles_description like '%" . $keywords . "%' or ad.articles_head_desc_tag like '%" . $keywords . "%' or ad.articles_head_keywords_tag like '%" . $keywords . "%' or ad.articles_head_title_tag like '%" . $keywords . "%') order by ad.articles_name ASC");
} else {
$search_query = tep_db_query("select ad.articles_name, a.articles_id, ad.articles_description from " . TABLE_ARTICLES_DESCRIPTION . " ad inner join " . TABLE_ARTICLES . " a on ad.articles_id = a.articles_id where a.articles_status='1' and ad.language_id = '" . (int)$languages_id . "' and (ad.articles_name like '%" . $keywords . "%' or ad.articles_head_desc_tag like '%" . $keywords . "%' or ad.articles_head_keywords_tag like '%" . $keywords . "%' or ad.articles_head_title_tag like '%" . $keywords . "%') order by ad.articles_name ASC");
}
I cannot fully test it because I do not use two languages on any of my sites. If it works for you, please let me know and I'll add it to the package.