In English, people would not usually say "We meet each other Sunday". If they mean a regular meeting every Sunday, they would say "We meet on Sundays." If they mean a specific meeting this Sunday, they would say "We will meet on Sunday." Sometimes they drop the "on".
The term "meet each other" would normally only be used for the first time people are introduced. If you are scheduled to meet someone you don't know, you might say "We will meet each other on Sunday."
Thanks for the comment below, roselaw, and others further down. I didn't know that was ok in US Eng. I am fine with US Eng being the main thing, but I didn't even recognise the construction as something that existed in any brand of English.
It simply appeared to me to be very poor English, and, more importantly, the meaning is obscure- that's why I ended up in the discussion. The translation made no sense from my experience of English as a native speaker and former teacher of it, and so I couldn't understand the Italian. It's not like I'm trying to be difficult and not accept a version of English different to my own.
Giving it the answer it wanted to complete the set of exercises was very painful- it feels like I'm writing something like "Where are you am do is has gone?" that kind of level of cringe and feeling of not making sense :)