Is there a way to show the day of the week for a card's due date? For example, "Mon Jan 14" instead of just Jan 14?
Not currently, it always to the US format (month, day).
While @SteB is right (you can't view due dates in the requested format), I'll just add that if this is a feature request you'd like to make, you can email the developers at firstname.lastname@example.org.
Describe the current as-is state and how you'd like it to behave in the future.