I'm guessing you've had a look at https://www.deepl.com/translator ? I don't speak Portuguese so I can't judge, but it explicitly offers European Portuguese as a translation target, and their other translations are usually top-notch.
Douglas Hofstadter's test sentence:
In their house, everything comes in pairs. There’s his car and her car, his towels and her towels, and his library and hers.
DeepL translation:
Dans leur maison, tout vient par deux. Il y a sa voiture et la sienne, ses serviettes et les siennes, sa bibliothèque et la sienne.
DH translation:
Chez eux, ils ont tout en double. Il y a sa voiture à elle et sa voiture à lui, ses serviettes à elle et ses serviettes à lui, sa bibliothèque à elle et sa bibliothèque à lui.
As a French native, I can tell you that DH's translation is great. And DeepL's reply is still something you can recognize at automatic translation at first sight.
Don’t get me wrong, more often than not, current MT tools give good enough results to understand the treated topic. But that’s still hideous translations. I wouldn’t buy a book translated through them for example.
Is there a reason why "sa bibliothèque à elle et sa bibliothèque à lui" is a better translation of "his library and hers" than "sa bibliothèque et la sienne"? I know it's just a word-for-word translation, but the latter seems more natural, and the former unnecessarily verbose. Especially in context, where the original English deliberately interrupts the pattern of "his car and her car, his towels and her towels", as a matter of prosody.
Not that I'd expect the computer to "know" that. I'm just curious, as a French learner, about why DH's translation is better.
> Is there a reason why […] is a better translation […]?
What do you mean with "a reason why"? From a synchronic or a diachronic point of view? Yes, there are reasons that linguists can provide. But for the mere layman, it will simply be weird to encounter such an utterance, full stop. Not that your question is non-sense, I would rather simply expect most people to be unable to tell you why despite they know it sounds weird.
> I know it's just a word-for-word translation, but the latter seems more natural, and the former unnecessarily verbose.
What you mean with "seems more natural", is that it sounds closer to what you are accustomed to in your own language. French is generally more verbose than English, especially in usual written form.
Now, as your "why" is nontheless completely legitimate, here is one explanation .In the case of "sa bibliothèque et la sienne", unlike in English which insist on the possessor (his/her takes the gender of the one who owns the object), French insists on the possessed (sien/sienne takes the gender of the object which is possessed, and every substantive have a gender). So would you translate "her library and his" in the same way, you would end up with the very same translation "sa bibliothèque et la sienne". On the other hand "sa bibliothèque à elle et sa bibliothèque à lui" would preserve the information of who owns each library.
Would you really mind to comes that is as close as possible to the original prosody, you might use "sa bibliothèque à lui, et elle la sienne."
The service you link to doesn't seem to offer a translation from and to Greek. It's also missing many other EU languages, e.g. Swedish, Danish, Hungarian, Zcech, etc.
Edit: to clarify, other translation servies I've used, notably Google, do translate from and to Greek but make a meal out of it.
