I don't know if my language grammar rules (Italian) are different than English, but I've always seen spaces before and after em-dashes. I don't like the em-dash being stuck to two unrelated words.

That's because in Italian, like in many other European languages, you use en-dashes to separate parenthetical clauses. The en-dash is used with space, the em-dash (mostly) without space and that's why it's longer. On old typewriters they were frequently written as "--" and "---" respectively. So yes, it's mostly an English thing. Stick to your trattinos, they're nice!

It's a US thing