Stack Exchange sites use ISO-8601 date formats, and if they don't, it's considered a bug if the site uses the date format commonly used in the USA. It also uses the 24 hour clock, and it's again considered a bug if this isn't the case.
So the SE sites don't use the date and time formats commonly used in the USA (where SE Inc. resides) and even shows times in UTC, which is a very good thing, considering the international and culturally diverse audience of the sites (well, only second to individually configurable preferences I guess).
Unfortunately, what is not considered are week boundaries defined in the same standard, i.e. what day of the week is considered to be the first weekday.
These are implicitly shown in the Users tab, and explicitly in the User Reputation Leagues. Today I earned 130 rep, and that's my total for "this week":
In many countries across the world, and in the mentioned international standard ISO-8601, Monday is the first day of the week, rather than sunday. It appears that only the USA, Canada, Japan and Israel consider Sunday to be the first day of the week.
Now we have
- International standard based date format, rather than mm/dd/yyy commonly used in the US
- International standard based time format, rather than the AM/PM used in the US
- Week boundaries as only used in the US, Canada, Japan and Israel.
This is inconsistent and should be fixed.