This is really inelegant, but maybe you could check the last inputted character's character code and see if it is higher than the character code for English characters (usually 60-100):
$('textarea').on('keyup',function(e) {
var value = $(this).val(),
length = value.length,
lastChar = value.substring(length-1, length),
charCode = lastChar.charCodeAt(0);
if (charCode > 200) {
// $.ajax()
}
});