As site admin, when I browse a user's account details page, the dates section will vary from user to user:
With user jmasson, the dates are shown in "relative first, absolute shown" format, and are in French
With user abrenning, they are in "absolute first, relative tooltip" format, and are in English.
This is because the code (wrongly) uses the displayed user's preferences. Thus, the format will change for each user. It should instead use the site administrator's preferences, so that the format does not change.