The singular Sei così gentile! and the plural Siete così gentili! are Italian equivalents of the English phrase "You are so nice!" Context makes clear whether one "you" (case 1) or two or more "you all" (example 2) suits. The respective pronunciations will be "sey ko-SEE djen-TEE-ley" in the singular and "SYEH-tey ko-SEE djen-TEE-lee" in the plural in Italian.
"So adorable!" in English is Cosí adorabile! in Italian.
"You are so handsome!" in English is Sei così bello! in Italian.
"So good!" in English means Che bello! in Italian.
"So are you" in English means Anche tu lo sei in Italian.
"I am so tired!" in English is Sono così stanco! in Italian.
Così felice! in Italian is "So happy! in English.
"You look so sexy!" in English is Sembri così sexy! in Italian.
"I'm so glad!" in English is Sono così felice! in Italian.
"You're so handsome!" in English is Sei così bello! in Italian.
no lo so
"You're not so bad!" in English is Lei non è così cattivo! in Italian.
sei un figo