вота из чулана приволок ... делал простую замену тогда ...
дай бог памяти в каком это году
var href="русскоеблалала";
var abcr = new Array("А","Б","В","Г","Д","Е","Ё","Ж",
"З","И","Й","К","Л","М","Н","О",
"П","Р","С","Т","У","Ф","Х","Ц","Ч","Ш","Щ",
"Ъ","Ы","Ь","Э","Ю","Я","а","б","в","г","д","е","ё",
"ж","з","и","й","к","л","м","н","о","п","р","с","т","у",
"ф","х","ц","ч","ш","щ","ъ","ы","ь","э","ю","я");
var abci = new Array("%C0","%C1","%C2","%C3",
"%C4","%C5","%A8","%C6","%C7","%C8","%C9","%CA",
"%CB","%CC","%CD","%CE","%CF","%D0","%D1","%D2","%D3","%D4","%D5","%D6","%D7",
"%D8","%D9","%DA","%DB","%DC","%DD","%DE","%DF","%E0","%E1","%E2","%E3","%E4","%E5","%B8","%E6","%E7","%E8","%E9","%EA","%EB","%EC","%ED","%EE","%EF","%F0","%F1","%F2","%F3","%F4","%F5","%F6","%F7","%F8","%F9","%FA","%FB","%FC","%FD","%FE","%FF");
for (i=0; i<abcr.length; i++) { while (href.split(abcr[i]).length>1) href = href.replace(abcr[i], abci[i] )};
alert(href);