CafeTran

Seldom. Life's too short for that.

本気ですか。

Good to hear!

日本語の翻訳を始めたいとずっと思っていました!

All three together I think, but especially with long sentences. In the end, it takes longer than translating from scratch with the help of manual electronic dictionaries. 

Perhaps the training corpus is too small (not very likely).

Perhaps the edit distance from JP to IT via EN is too big?

Perhaps the used pattern recognition algorithms aren't suited for character-based languages?

Tried Japanese: it's better than Google Translator, but almost equally useless.