#Pyth, <s>9</s> 7 bytes

Thanks to @Maltysen for saving 2 bytes!

    mlc.Bd8

[Test suite][1]

Converts every character of the input to it's binary representation and then splits this into chunks of length 8. The number of those chunks is then the amount of bytes needed to encode that character.

  [1]: http://pyth.herokuapp.com/?code=mlc.Bd8&input=%22t%CA%83a%CA%8A%22&test_suite=1&test_suite_input=%22%21%22%0A%22Ciao%22%0A%22t%CA%83a%CA%8A%22%0A%22Ad%C3%A1m%22%0A%22%C4%89a%C5%AD%22%0A%22%E3%83%81%E3%83%A3%E3%82%AA%22%0A%22%22%0A%22%21%C2%B1%E2%89%A1%F0%A9%B8%BD%22&debug=0