Solved
Format of a!datefield
Although the user's locale is set to el (Greek), the a!dateField() displays the date in mm/dd/yyyy format instead of dd/MM/yyyy.
Why is that? How can I change that?
I suggest to raise an Appian Support ticket for this. Looks like the notation mm/dd/yyyy in placeholder is incorrect though the value saved is in dd/mm/yyyy format when I did a quick test!
Happy to help. Even happier to optimize.