Parallels Desktop 5 for Mac - How setup different language?

Good morning to all!
Last days, as a birthday present, i've received a copy of Parallels Desktop 5 for Mac.
The main language of the software is Italian (i live in Italy) and i'd like use it in English (for business i use all of my Mac's software in English). I've presupposed, as almost all of Mac's software, that Parallels software using the host's OS main language, but the situation is not like this...
I've downloaded from Parallels web site a copy of English's trial version but my license key related to the Italian version of the software does not work with English version.
Could you please help me?
Thanks in advance,

Mariano