"Stephanus and Corinna study Latin."
Translation:Stephanus et Corinna linguae Latinae student.
From what I've read in other threads here, it's because you need "linguae". In Latin, you can't just say "Latin", you have to say "the Latin language" every time. Stephanus et Corinna linguae Latinae student. The way I saw it described elsewhere was that, in Latin, it's considered an incomplete thought, the same way as "I am a tall" would be considered an incomplete thought in English. The listener would be like, "... a tall what?"