l'abito non fa il monaco betyder på engelska

clothes don't make the man▼phrase
[UK: kləʊðz dəʊnt ˈmeɪk ðə mæn] [US: kloʊðz ˈdoʊnt ˈmeɪk ðə ˈmæn]

the cowl does not make the monk▼(the superficial trappings of something are unrelated to its true essence)
phrase
[UK: ðə kaʊl dʌz nɒt ˈmeɪk ðə mʌŋk] [US: ðə ˈkaʊl ˈdəz ˈnɑːt ˈmeɪk ðə ˈməŋk]

you can't judge a book by its cover▼(it is not possible to judge things by external appearances alone)
phrase