Translation:I dislike English because it isn't easy at all.
If we were to take at all completely literally, I would agree. But in English, or at least any dialects of English I'm familiar with, at all doesn't mean absolutely or completely; it is simply an intensifier. Not easy at all means the same thing as very not easy, but you can't say very not easy, so you have the at all expression.
-qu' is completely appropriate here.
"Very not easy" sounds terrible in English and if I we're teaching English I would refuse to accept it. However, since I am teaching Klingon, that poor English translation shows a very good grasp of the Klingon, and I can mark it so it is never shown to a student unless they type it first, I've added it to the accepted translations.