For those of us who aren't American English speakers and for whom gross refers to certain financial matters, what would the best superlative adjective to use instead? I tried 'most horrible', but I am loath to use a term like 'yuckiest', considering that I am over five years old. Maybe 'most disgusting'? Just like 'ekelig' auf Deutsch, it's a tricky one to translate.
American English speakers and British English speakers live thousands of miles apart. Why do some English people seem so put out by seeing that the two languages are evolving differently? If you think you know a language because of what you see through pop culture, you are going to miss a lot. American English has several meaning for the word "gross." Twelve dozen, disgusting, and huge are a few that come to mind. When you come across a word whose translation you disagree with, report it. The Norwegian Duolingo people are responsive and open-minded. It may be the best group of people the company has working for them.
You seem to be confusing comparatives with superlatives. "Ekleste" falls firmly in the latter category, and translating a superlative with a comparative is out of the question.
If you use "gross" in the British English sense, which is of course not an option in this particular sentence, it would have no comparative or superlative form.