Translation:The Kovács family's dog runs down the street, to the lake.
No, I am not an insider. But I did read up on the incubator blog while all of us were waiting for this. Many of these things were mentioned there. And I see improvements here and there. And I am receiving the occasional confirmation of my accepted translations.
It has not been updated since the first week of beta.
You can't report your sentence if it's been accepted, unfortunately.
I'd argue that "the Kovacs's dog" isn't correct anyway. If it's a family dog, you'll make is a possessions of all family members, so you'll say something like "the Millers' dog" or "the dog of the Millers". "The Miller's dog" would be the dog of only one Miller.
So in this case it would rather be... "the Kovacses' dog"? However you pluralise "Kovacs" in English.
your correct that the plural of Kovacs would likely be Kovacses. The other fun part of this sentence is the possession - there is debate in English about whether to add an s after the apostrophe for nouns ending in "s". I was taught in public school to not add the S, but in university and law school they prefer it. It is also perfectly correct to use the singular last name to refer to the entire family. I believe this is at least partly because when referring to family's possession, you always use "The" - you wouldn't use this if reffering to a single person. "Kovacs' dog" is a dog that belongs to one person you call by their last name, and "The Kovacs' dog" belongs to the family. However, one is still free to pluralize the family if you want to, like you did.
Because of this, you could refer to this dog in four different ways: "the Kovacs' dog," or "the Kovacs's dog," or "the Kovacses' dog," or "the Kovacses's dog."
Forza, your very last example isn't correct. It's valid to use either a lone apostrophe and " 's" for a singular noun that ends with 's'. However, if a plural noun ends with 's', only the lone apostrophe gets added:
the princess' dress or the princess's dress - the dress of the princess
the princesses' dresses - the dresses of the princesses