I think this is a bug... I changed my Formatting Locale to Japanese for testing, and the users table seems to display the "Date Created" value by each user's formatting locale, rather than the formatting locale I've set on my account.

Additionally, I think the week start date values should be updated when the formatting locale is changed. Currently it only updates after saving and refreshing the page:

Date values are rendered using craft\i18n\Formatter::asTimestamp() (same function that the |timestamp filter uses), so the different formats you are seeing there are due to the different time scales the dates have relative to the current date/time. If each of the Date Created values were more than 7 days prior, they would each be output using a Japanese date format.
Additionally, I think the week start date values should be updated when the formatting locale is changed. Currently it only updates after saving and refreshing the page:
Can you post a new issue (enhancement) about that?
Hmm it seems weird to me that the weekday is translated to the formatting locale setting but "today" and "yesterday" stay in English regardless? Especially when comparing the dates in a column.
Agree it’s a bit weird. Happening because weekday names are sourced from the locale data, whereas “Yesterday” is coming from the message translations (which are correctly sourced based on your preferred _language_ rather than your preferred formatting locale).
Just fixed this by changing asTimestamp() to pull the week day name from the application language, rather than the formatting locale.
Would that affect the date-picker calendar UI?

Maybe should print the full formatted date even when it's within the last week?
Doh, yeah the same change needed to happen there as well. Done.