Answer: You don't. You go for what's ever cheapest because that's the only thing you can judge (unfortunately the amount is in Euros so you can't even compare that amount to the American price you would pay) or you pick the carton that expires on 5/6/10 (if you remember that in Europe this means the fifth of June and not the sixth of May, which was two weeks ago). So the "melk" you choose expires after all the others. Is that normal? I don't know, you might have just purchased yourself some soy "melk."
I'd forgotten the culture shock we experience when we went to Paris some five years ago now, but it has all come rushing back to me in many ways, the most prevalent being my trip to the grocery store yesterday. It's intimidating being in a different country and not speaking the native language, even when everyone knows how to speak your language.
Then of course there are more cultural things than lack of knowledge of language. I personally believe the way a society eats is revealing of it's culture. If you can master the culinary rituals, you can master just about anything and look like a pro, even if you're speaking English while doing it. Unfortunately many times we must fall and bump our heads before we take those first steps. So it's ok to loiter in front of a restaurant to see if people just sit down randomly at the outdoor cafes, all the while knowing everyone has spotted you as an American, and try to enjoy sitting at your table and talking with your friends even though you finished your meal half an hour ago. We rush too much anyway.