I have heard that it is quite a hard task to translate Kant's ideas from German. Is it better to read the Critique of Pure Reason in English or Italian? I have heard some people say that English is better because the languages are more similar.
It's not necessarily the language, but the edition you should keep an eye on.
As I wrote here, translations of Kant are problematic in and of themselves, partly because even German native speakers might understand some key points quite differently. But in English, the Cambridge Editions are quite a good standard and unmatched so far.
When it comes to Italian, I do not have any substantive experience when it comes to Kant translations. What I do know, though, is that there is a lively philosophy community studying German philosophy and that oftentimes, very complicated texts have good translations into Italian way before an English translation with more or less questionable quality is available (speaking of Dilthey, Scheler, Plessner, Gadamer here). This makes me think that any recent Italian translation should have quite a decent quality as well, but I cannot vouch for it. Asking an Italian Kant scholar might help here.
This page shows recent translations for each and every single text Kant ever wrote. It seems that, just as I expected, there are recent Italian translations for many of them available.
That being said, it also depends on your level of proficiency. If you are Italian and not wanting to dive deep into English secondary literature, an Italian translation may be better to get a basic understanding of Kant since there may always occur a loss of meaning when reading in a secondary language.
I suppose I would have to suggest it makes the most sense to read it in the language YOU are most fluent in comprehending.