I would like to be able to specify a date, without having to worry about what date format a reader might expect to see it in, since I work on a project which has members in several different countries.

Confluence already includes this feature: https://support.atlassian.com/confluence-cloud/docs/insert-elements-into-a-page/#:~:text=create%20inline%20code.-,Date,Type%C2%A0//%C2%A0to%20bring%20up%20a%20date%20picker.,-Decision. Something similar to this could work.

This would also give these the dates a consistent appearance throughout Jira issues, which I believe will make them easier to read and understand.

Each user would then have the ability to set their own default date formats, unless there were a way to glean this from the browser instead. If desired, also give the ability for administrators to set a default format for the whole Jira instance or Jira project