Is there a firebird.msg file in Italian?
Not that I know of.
In the source there is a directory \src\msgs where the firebird.msg is build.
There are translations in German en French. Not any other.
(Maybe some third party has translated them once.)
You could also make your own translation. But you can also catch exceptions program wide and translate them then.
Besides, for most messages I would prefer the original English ones.
Otherwise it's a lot harder to search the internet for solutions when you get those in another language.
Only for the most common error codes (like DB not found and Record liked and some others) I provide translations.
Edit: O, and IB EXpert had a tool for directly translating the Firebird.msg.
http://www.ibexpert.net/ibe/index.php?n=Doc.LocalizeIBMessages