Does the word Víkend come directly from English?
Yes, we just write it phonetically.
See, I translated this as " thanks have a nice weekend" and the answer is saying that its " thanks and a nice weekend." So I guess the direct translation is what it wants?
You are missing "and" for the Czech "a". "Thanks and have a nice weekend." is accepted.
Is the word víkend common in Czech?
I tried "good weekend". But it didn't work. Now I know.
This time it accepted "good weekend." Guess I didn't learn the first time.
But, which is correct?
You should report the complete sentence. "good weekend" is accepted.
I (native AmE) would say that "Have a nice weekend" and "Have a good weekend" are probably used with about the same frequency, at least in the US, and both are accepted.
So do Czech people really says just "hezky víkend" and "have" is implied or you need to say Czech word equivalent for "have"?
The having is implied and actually including it is an ugly anglicism. There is no explicit having in Dobré ráno, Dobrý den, Dobrý večer and Dobrou noc either.
Can you also say Děkuji a přeji hezký víkend?
Yes, you can, but it is something extra, not the default form. Therefore, I would not accept it here (přeji = I wish you).