Unfortunately it is not possible in the default X-Cart.
But this feature can be custom programmed.
You should alter the "modules/Extra_Fields/extra_fields.php" script and replace this code:
PHP Code:
$smarty->assign('extra_fields', $extra_fields);
with this one:
PHP Code:
if (in_array(AREA_TYPE, array('C', 'B'))) {
foreach ($extra_fields as $ef_k=>$ef_v) {
if (preg_match("/\{[$]{1}lng\.([a-z_]+)+\}/i", $extra_fields[$ef_k]['field_value'], $match)) {
$extra_fields[$ef_k]['field_value'] = str_replace($match[0], func_get_langvar_by_name($match[1]), $extra_fields[$ef_k]['field_value']);
}
}
}
$smarty->assign('extra_fields', $extra_fields);
Note: use FTP to edit the PHP scripts.
Alternatively you can
apply the attached Patch.
After the patch is applied you should be able using e.g. "{$lng.lbl_login}" as extra field value.