Convert sign character to unsign character, such as: Nguyễn to nguyen

Convert Sign to unsign character.gs

function convert(str){
  str = str.replace(/[^A-Za-z0-9\-_]/g, function(ch) {
  // Character that look a bit like 'a'
  if ("áàãạảâấầẩẫậăắằẳặẵ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'a';
  }
  if ("ÁÀÃẠẢÂẤẦẨẪẬĂẮẰẲẶẴ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'a';
  }
  if ("đ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'd';
  }
  if ("Đ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'd';
  }  
  if ("eéèẻẽẹêếềểễệ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'e';
  }  
    if ("EÉÈẺẼẸÊẾỀỂỄỆ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'e';
  }  
  if ("iíìỉĩị".indexOf(ch) >= 0) { // There are a lot more than this
    return 'i';
  }
    if ("IÍÌỈĨỊ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'i';
  }
  if ("oóòỏõọôốồổỗộơớờởỡợ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'o';
  }
    if ("OÓÒỎÕỌÔỐỒỔỖỘƠỚỜỞỠỢ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'o';
  }
  // u
  if ("uúùủũụưứừửữự".indexOf(ch) >= 0) { // There are a lot more than this
    return 'u';
  }
  if ("UÚÙỦŨỤƯỨỪỬỮỰ".indexOf(ch) >= 0) { // There are a lot more than this
    return 'u';
  }  
  /* ...long list of others...*/
  // Default
  return '';
});
  return str;

}