I have found a way! Thanks to DJDavid98 that gave to me some clues.
var tmp = $('#banDateOneReal').data('DateTimePicker').getDate();
$('#banDateOneReal').data('DateTimePicker').destroy();
$('#banDateOneReal').datetimepicker({
language: 'en',
});
$('#banDateOneReal').data('DateTimePicker').setDate(tmp);
This code is going to destroy the datepicker item and create a new one with the good language.
There is no function yet to refresh it without destruction.