When Chinese speakers read Arabic numbers, do they still read them in Chinese?
I'm a native speaker. I'll read "我(wo) 想(xiang) 要(yao) 三(san) 百(bai) 二(er) 十(shi) 一(yi) 個(ge) 餃(jiao) 子(zi)".

BTW "321餃子" doesn't make sense. "321個餃子" would be correct because you need the unit "個".