Yeah i managed to get it to save aswell. Had to change the prepareMultilanguageData function to something like this:
function prepareMultilanguageData(form){
form.find('.multilanguage-input').each(function(i, e){
content = '';
for(i=0; i < languages.length; i++){
var tmpId = jQuery(e).attr('id');
val = jQuery('div[rel='+jq(tmpId)+']').find('#'+languages[i]+'_'+jq(tmpId)).val();
if(jQuery.trim(val) != ''){
content += '<!--:'+languages[i]+'-->'+val+'<!--:-->';
}
}
jQuery(e).val(content);
});
}