Don't know, but in Swedish it's our version of "Bless you". As in you say "prosit" after someone sneezes. So this picture confused me for a few seconds or so, as I was trying to figure out that this had to do with sneezing...
"Ein Prosit" is literally used as a toast, sometimes with something following it (a very popular song goes "Ein Prosit der Gemütlichkeit", which is traditionally sung at the Hofbräuhaus or at Oktoberfest). I've never seen "prosit" refer to "progress" in any way, at least not in Germany, which is clearly the language of choice in this picture (aside from the text there's also the bavarian flag-pattern on her pantyhose and she's holding a traditional bavarian beer mug).