Sei bella! in Italian means "You're beautiful!" in English.
Ti sei fatta bella! in Italian means "You've prettied yourself up!" in English.
Sei la ragazza più bella! in Italian means "You're the most beautiful girl!" in English.
"You are prettier!" in English is Tu sei più bella! for a female and Tu sei più bello! for a male in Italian.
"You are a beautiful person!" in English is Sei una bella persona! in Italian.
"You're beautiful and amazing!" in English is Sei bella e sorprendente! in Italian.
"You are a beautiful child!" in English is Sei un bel bambino! to a male and Sei una bella bambina! to a female in Italian.
Quando scrivi in italiano sei ancora più bella in Italian means "When you write in Italian you're even more beautiful" in English.
Chi sei? in Italian is "Who are you?" in English.
"Beautiful, where are you from?" is an English equivalent of the Italian phrase Bella, di dove sei? The question translates literally as "Beautiful, of where are you?" in English. The pronunciation will be "BEL-la dee DO-vey sey" in Pisan Italian.
To a boy - "Tu sei piu bello" To a girl - "Tu sei piu bella"
Tu sei il mio cuore, bella rosa nera! in Italian means "You are my heart, beautiful black rose!" in English.
Sei bravo! in Italian means "You're good" in English.