Control Panel Date Picker: Inconsistent Date Format

Question

In my plugin I have a datetime field defined in the settings template:

{{ forms.dateTimeField({
    label: "Ends at"|t('optimum'),
    instructions: experiment.isNew ?  'Defaults to 30 days from now' : '',
    id: 'endAt',
    name: 'endAt',
    value: experiment.endAt ?? defaultEndAt,
    errors: experiment.getErrors('endAt')
}) }}

When I use the picker I get a date in mm/dd/yyyy format. This is then sent to the backend and parsed back to a Carbon instance.

This is what I'm seeing on my end:

However, it seems that the date format is not consistent across installations. As you can see in this issue, the user reports that the datepicker populates the date in dd/mm/yyyy format, which breaks the functionality as the backend is expecting mm/dd/yyyy format.

How can I enforce a uniform format?

Answer 1

All dates in the control panel are rendered localized as per the logged-in user's "Formatting Locale" user preference, or their "Language" setting if they haven't set a preferred locale.

For users who haven't set a preferred locale or language, Craft will fall back to the locale defined in the defaultCpLocale setting.