"Are you afraid for your wife?"
Translation:Bojíte se o svou manželku?
if "My sister is afraid of mice" is translated as, "Moje sestra se bojí myší", why "Are you afraid of your wife?" can't be translated as, "Bojíš se své ženy?"
Here we have afraid FOR, not afraid OF. Please do read previous discussion before asking like this. See the answer by Jamie08MD.
Oh, sorry! I didn't notice it was "for" in the English sentence, and thought the other person was simply asking how to say that. Thank you very much for the reply!
Later on there is also a sentence, "Bojím své manželce" which is translated as "I'm afraid of my wife". So why Genitive without a preposition can't be used here?
"Bojíte se své manželky?" [bát se + genitive] - Are you afraid of your wife?
"Bojíte se o svou manželku?" [bát se + o + accusative] - Are you afraid for your wife? This second sentence is asking if you're concerned, worried about her safety (that something bad might happen to her).
Hope it is clearer. :-)