how to translate the fields

function getEcommerceFields() {
      $fields = new FieldSet(
         new HeaderField('Personal Information', 3),
         new TextField('FirstName', 'First Name'),
         new TextField('Surname', 'Surname'),
         new TextField('HomePhone', 'Phone'),
         new TextField('MobilePhone', 'Mobile'),
         new EmailField('Email', 'Email'),
         new TextField('Address', 'Address'),
         new TextField('AddressLine2', ' '),
         new TextField('City', 'City'),
         new DropdownField('Country', 'Country', Geoip::getCountryDropDown(), self::findCountry())
      );
and so on like amount, i have multilingual site