When you are changing users language from UK_GB to US at Users Settings -> Profile, date format is not changed. UK date`s format is like d-m-Y, and US - m/d/Y.
Steps to reproduce:
- Validate, that date format for UK_GB is displayed correctly according to UK_GB time format(d-m-Y)
- Change Users language from UK_GB to US at Users Settings -> Profile
- Validate date`s format