Thank you Steve.
It is hardcoded, but can be overriden easily.
The relevant lines in the class classes/XLite/View/FormField/Select/Title.php are
Code:
protected function getDefaultOptions()
{
return array(
'Mr.' => static::t('Mr.'),
'Ms.' => static::t('Ms.'),
'Mrs.' => static::t('Mrs.'),
);
So just write a class that extends Title.php and override the method getDefaultOptions(), add labels and translations if necessary, and you will be fine.