Feature summary (what you would like to be able to do and where):
Dates in Swedish like
"22 august 29" can be hard for the user to parse because we are used to seeing dates year>1000.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
I suggest that Wikibase display the ISO date in a tooltip onmouseover

Benefits (why should this be implemented?):
Everyone entering dates to make sure it is correctly entered.