"You write Spanish well?" This is pretty close to what they wanted.
"You write Spanish well" is still a translation with the same meaning as "You write well in Spanish"
It has the same meaning, agreed, but I wouldn't say that it is a translation of the above. Such a simple sentence, no need to alter the structure when translating into English.
Why more acceptable? What is wrong with "you write well in Spanish"?
You write in Spanish well seems like good English to me. You ride the horse well or You ride well the horse? Hmmm.
It's important to remember other languages often structure differently than english. Word orders wii typically differ from our english. If learn to shift into their pattern it makes thins flow easier