Input multilingual text in a form...

Hello all,

If someone input characters from various languages into a form in a browser and  form's encoding is in UTF-8, what is the encoding of text insert? Is UTF-8 or something else? 
I want to store this text as unicode (UTF-8) in a database, but if this text is not UTF-8, i need a converter from all other encoding to UTF-8?

Numeric reference of characters in ISO-8859-1 is the same of Unicode, not only for ASCII character (0-127)?
I think no but i'm not sure.

Any link to further information would be greatly appreciated.
Thank you!

Donatella