Why is "a" necessary here? "I don't like a sheep" doesn't sound right.
Very odd! Better would be either of:
(But then again, dafad/dafaden also means 'wart' ...)
It shouldn't be necessary, but it is technically a way of translating the sentence, even if it sounds a bit weird.
That's why I'm confused why it states it's obligatory- it doesn't really make sense in English, and not many of the other statements have been extremely analysis about translation.