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.
"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.
"You are so handsome!" in English is Sei così bello! in Italian.
Così felice! in Italian is "So happy! in English.
"You're so handsome!" in English is Sei così bello! in Italian.
"I'm so glad!" in English is Sono così felice! in Italian.
"You look so sexy!" in English is Sembri così sexy! in Italian.
no lo so
"You're not so bad!" in English is Lei non è così cattivo! in Italian.
sei un figo