Apologies I responded so late.
I have reviewed all the problems and managed to solve them.
"edit many files for string translation (not only in english)"
- Please send them to me, I will compare the files to improve the plugin.
"add italian translation if you prefer i can send you on email the modified files for next update."
- Please, my email is email@example.com
"Actually i see that fileds validation during checkout progress doesn't work... now i can place an order with empty customer fileds and the system give to me this error: UnexpectedValueException: The Response content must be a string or object implementing __toString(), "boolean" given. How i can fix this?"
- I have managed to review this problem and I have not been able to get that error, could you send me a capture or the error log? I promise to solve it as soon as possible.