It's neither lr=_lang_xx nor lr=xx but lr=lang_xx (see here).

However, the [ lr => 'lang_it' ] notation seems to be ignored by the Google::Search API. Try this:

my $search = Google::Search->Web( query    => { q  => "site:sunrise.ch
+",
                                                lr => 'lang_it',
                                                hl => 'it',
                                              },
                                  # key      => $your_google_api_key,
                                  # referrer => $valid_referrer, 
             );
[download]

...which works better.
You might also want to check $search->error and $search->error->reason ...

Hint: Suspected Terms of Service Abuse. Please see http://code.google.com/apis/errors and key/referrer-comments above...