"They eat the fish."
Translation:Mangiano il pesce.
le - il - la - l = the - what are the rules for the appropiate usage?
In this case, if you state "the" in English, I would keep it in Italian. If you say that they eat "that" fish, it's better to keep the article. It's my personal opinion, anyway.
"Mangiano pesce" would mean "They usually eat fish"
"Mangiano il pesce" = "They eat a specific fish" or "They usually eat fish"
"...if you state "the" in English, I would keep it in Italian."
Agreed! The use of the determinative article in English is less casual. If "the" shows up in the original sentence, you'll most likely need it in the Italian translation. There are, however, a small handful of idiomatic exceptions that you'll encounter as you go along.