UI date formats are wrong for most of the English-speaking world

Steps to reproduce:

1. Create an event in the admin UI

Actual Results:

Dates shown in m/d/yy format

Expected Results:

All English-speaking countries except US (and maybe Canada) use d/m/y

https://en.wikipedia.org/wiki/Date_format_by_country

Perhaps the admin UI needs an English (UK) language selection.