From Python can be done this way:
request.user.message_set.create(message=_('You did it!'))
From javascript:
notify.show(gettext('You did it')); //will hang until deleted or the page reloaded
notify.show(gettext('Yeah'), true); //in this case message will flash and fade out
The fade-out effect will be available in the future release, probably 0.7.45.
Caveats - (1) we'll have to switch to using another method of messaging, because this one will be removed from the future Django releases; (2) javascript API can change in the future.
A separate question is - which messages you'd want to show and in what circumstances...
Encouraging messages are great, but should not be shown way too often.
What do you mean by "status message"? Are you talking about the banner that appears at the top of the page when you receive a badge?