function chg_lang (lang) {
	var full_url = parent.location.href
	var q_index = full_url.indexOf("?")
	if (q_index==-1) {
		q_index = full_url.length
	}
	var front_part = full_url.substring (full_url, q_index);
	var dot_index  = full_url.indexOf(".", q_index-5);
	var query_part = full_url.substring (q_index, full_url.length);

	if (lang=="en") {
		new_front_part = front_part.substring(0, parseInt(dot_index)-2) + "" + front_part.substring(parseInt(dot_index), front_part.length)
	} else {
		new_front_part = front_part.substring(0, parseInt(dot_index)) + "_c" + front_part.substring(parseInt(dot_index), front_part.length)
	}
	
	if (query_part=="") {
		new_full_url = new_front_part
	} else {
		new_full_url = new_front_part + query_part
	}
	parent.location.href=new_full_url
}