I respectfully disagree though I should have capitalised less carelessly - 'Sister studies' feels to me fine without an article - compare: 'Father arrives', 'Mother disapproves'.
TBH to my ear, the sentence 'The sister studies' is itself rather awkward and contrived, and perhaps this is the issue. 'Sister' really needs some clarification of the relationship (presumably a pronoun rather than the article) - 'my sister studies', 'her sister studies' are much more plausible sentences. 'The sister studies' feels like a fragment of a sentence at best - in a lifetime, have you ever said this sentence?
So all in all, I still think 'Sister studies' is ok - because it reads implicitly as '(my) sister studies' or (eg of a nurse or nun) 'Sister (Mary) studies.
"Father" and "Mother" are often used as titles/names (like "Mommy/Mummy", "Daddy", etc.), which don't require articles, but I don't hear "sister" and "brother" used the same way (unless referring to a nurse/nun/monk, when I've only encountered it accompanied by a name unless directly addressing the relevant sister/brother).
I agree that "The sister studies" is kind of awkward, but it's difficult to come up with an English translation of the Latin sentence that doesn't, without adding in something like a possessive which isn't in the Latin.
Hospitals and convents are perhaps the only places you'd hear eg 'Sister is waiting for you', so I agree, but really I suspect all this is clunky maybe because it's something of a clunkily-chosen example phrase? "Livia studet" eg might have been clearer, and then get into family members only after introducing the possessives that make them clearer?
That maybe would have been better, but I assume the contributors probably had a reason for it. I'm not one of the regular contributors, just temporary help with the initial flood of reports, so I wasn't involved in the decision making process. :) At any rate, we're stuck with it until a new tree version is made now, which means we're also stuck with this kind of clunky sentence as at this point we don't have the vocabulary available to make anything better.
I see a / the bee •
I see the bees •
The bees make honey •
I see bees • [ Plural • Zero • Indefinite]
Bees make honey • [ Plural • Zero • Indefinite ]
English uses Zero Null Article Determiner before a mass noun and a plural noun, if the plural reference is indefinite • • Zero Article Thoughtco • • English Zero Article • • Zero Article Grammar • • English Zero Marking • • Zero Linguistics
Hm... wouldn't "my" be implied? I feel like it would be, but as it is not allowed right now while this is an early exercise, I'm not confident.
Very close of the French sœur. There's also a French adjective for "sœur", but almost nobody knows it, it's "sororal" = relative to the "sœur", to the sister. Sororal also exist in English, borrowed to the French.