I think you have to remove the accents first then do your RegExp.
You can use this function taht I found here :
function stripVowelAccent(str)
{
var rExps=[
{re:/[\xC0-\xC6]/g, ch:'A'},
{re:/[\xE0-\xE6]/g, ch:'a'},
{re:/[\xC8-\xCB]/g, ch:'E'},
{re:/[\xE8-\xEB]/g, ch:'e'},
{re:/[\xCC-\xCF]/g, ch:'I'},
{re:/[\xEC-\xEF]/g, ch:'i'},
{re:/[\xD2-\xD6]/g, ch:'O'},
{re:/[\xF2-\xF6]/g, ch:'o'},
{re:/[\xD9-\xDC]/g, ch:'U'},
{re:/[\xF9-\xFC]/g, ch:'u'},
{re:/[\xD1]/g, ch:'N'},
{re:/[\xF1]/g, ch:'n'} ];
for(var i=0, len=rExps.length; i<len; i++)
str=str.replace(rExps[i].re, rExps[i].ch);
return str;
}