1. My opinion is not to care about locale as for now since we usually only test in English and we are testing functionality instead of locale.

2. If locale is a real concern(but there are too many locale related issues in old codes, too), my suggestion it to use these
('xpath', '//form[@id="confirmation-message"]/button')
('css selector', 'form#confirmation-message button:first-child')
for _cancel_locator
('xpath', '//form[@id="confirmation-message"]/button[2]')
('css selector', 'form#confirmation-message button.danger')
However, there are some danger in there 2 methods, too.
Gaia code is using a tricky way to do so. I think asking developers for adding id might be a good idea instead.