I'm cooking a Romanian meatball soup for 60 people. How much of this soup do I need to feed 60 people?
After looking at many very similar recipes (in English) for Romanian sour meatball soup, or Ciorba de Perisoare, I'm inclined to think that this recipe does indeed make 5 liters.

Most all of the recipes I've looked at start with 500g of meat and have pretty much the same ingredient list. This recipe found on  CookingGlory says to :


  Add about 12 to 16 cups of water (about 4l). 


Based on this, I find it easy to believe that the finished soup would easily be 5 liters. (Also, in the translation provided by another user, it shows an amount of 5 liters.)

Also, translated from the link provided in the question:


  From the ingredients below we obtained a soup pot of approx. 5 L. You can reheat without problems and it is tastier every day (kept in the refrigerator lasts for 3-5 days).


And:


  I added the rest of the roots and I dropped everything with 4 L of hot water.


The recipe on Cooking Glory states that it makes 8 - 10 servings. 

So, basic math in hand, 5 L of soup, multiplied by 6 = 30 L of soup. That would give you sixty 500 ml portions.

The link above to the Cooking Glory page also gives a lot of information about the soup and its ingredients.