I'll be honest, the Ita version of 'Re:Zero' is a translation within a translation. Reading the Japanese light novels, the formal honorifics and narrative distance gave Subaru a different texture—he could be seen as more pathetic or pitiable. The Italian fan translation I read on a site aggregating those scans seemed to absorb more of that formality, keeping some of the honorifics and making the prose a bit denser.
By contrast, the official English release from Yen Press leans into a more localized, accessible voice. They smooth out the cultural bumps. The Ita version, at least the early fan ones I saw, sometimes kept the original sound effects with tiny translator notes, which the official English edition usually replaces with graphical ones. This creates a different pacing; the Ita one feels more like a document, the English one like a polished book.
There's also the matter of the afterwords. The author Tappei Nagatsuki's afterwords are full of his specific humor and meta-commentary. The unofficial Ita translations I've seen sometimes struggle with those tones, either becoming too literal and stiff or missing the self-deprecating jokes entirely. The official English ones capture his voice better, I think.
Ultimately, the biggest difference isn't in the plot, but in the feeling of the text. One feels like you're peeking at a raw cultural artifact with notes scrawled in the margin, the other like you're holding a commercially packaged product. I occasionally check the Ita version for specific phrases when a debate pops up in the Discord about a scene's interpretation.