你会不会说中文吗?
会 or 不会 means can or cannot?
你会说中文吗?
Can you speak in Chinese?
你会说中文, 会吗? can and can ( Chinese version)
Can you speak in Chinese?
Can you?
You can speak in Chinese, cannot you? can and cannot (English version)
他是不是中国人吗?
是 is a Chinese or 不是 not a Chinese
他是中国人,不是吗?
He is a Chinese, isn't he? ( English version and Chinese version)
^-^ It is up to you in Chinese, sometimes.