function lang_switch(lang){
	var new_src=window.location.search;
	if(new_src.length<2)new_src=new_src+'?lang='+lang;
	else{
		if(new_src.indexOf('lang')==-1)new_src=new_src+'&lang='+lang;
		else{
			if(lang=='eng')new_src=new_src.replace(/lang=pl/,"lang=eng");
			else new_src=new_src.replace(/lang=eng/,"lang=pl");
		}
	}
	window.location.assign(""+window.location.protocol+"//"+window.location.host+window.location.pathname+new_src);
}