I suggest you uninstall the versions in English or any other language.
Then run the file (it.exe) SketchUp Pro 8. ( For Windows)
The program will install itself in the Italian language.
You will still need to enter the purchased license key (being "pro").
For updates on SU2013 and SU2014:
Do not fail to install in other language versions.
Otherwise it will be, later, impossible to install Italian versions: there will be
several conflicts with the new platforms " Microsoft.NET Framework".
Always remember to make a backup on an external disk before installing
any program. (I use Acronis True Image).
Ciao