Aleram each language pack can define translations for the date, but they have no easy way of changing the formatting.
An extension could hack into Flarum's functions to change the formatting, but there's currently no easy way of doing it.
I think there will be changes to that in Flarum beta 14 since we're switching away from moment.js, but the general concept is still the same.
Most of Flarum's dates are rendered through the
humanTime helper, which we should try to make extendable by extensions.
PS: I believe violetamon 's comment from 2016 is actually incorrect. The
'14 part is the year 😉 But we have since switched to a more understandable format for English it seems.