Whichever language is set, the separator is irrelevant, '/', '-' or '.' all behave the same.
English (US) mm/dd/yyyy works as expected. It does show an error if incorrect value is entered, for example 25/12/2018.
English (UK) dd/mm/yyyy, Estonian dd.mm.yyyy and English (India) dd-mm-yyyy all accepted the normal values as expected. However, technically incorrect values - for example 12-25-2018 - were also accepted and had day and month values automatically switched.