Definition of it isn't done in English:

it isn't done

phrase

British
  • Used to express the opinion that a particular thing contravenes custom or propriety.

    ‘in such a society it is not done to admit to taking religion seriously’
    • ‘But someone should tell him that it isn't done to talk about one's son as one would about a prized racehorse at a stud farm.’
    • ‘In France bills are expected to be paid by the due date – it is not done to wait for the 'final warning' letter!’
    • ‘It isn't done to speak ill of the dead.’
    • ‘When you're pulling in $20 million a movie, it isn't done to ask exactly how long you spent in architecture school!’