Translation:I think the coffee there is the tastiest.
"I think that the coffee there is the most delicious," "I think that the coffee there is best," and "I think the coffee there is tastiest" were also rejected. None of these are bad translations.
Beyond that, I don't normally talk about coffee being the "tastiest" or "most delicious." I'd just say, "I think the coffee there's best."
Yes, in Duo-English you cannot say that you think THAT..... You have to leave out the THAT. I found in a previous exercise I was marked wrong for saying "think that" instead of just "think" followed by whatever the description of the thought was, so now I just omit the relative pronoun. I suggest you report it next time this happens to you.
It is 2020 and the English here is still from some 1845 dictionary. Never heard anyone referring to coffee as "the tastiest". I am sure this has been flagged countless times and still not fixed. And I am a paying customer so while I would agree that this might be OK for free, sadly not the case.
I want to say: I believe the coffee over there is the best. The way the sentence is phrased is quite opinionated, implying a gut feeling. The person is strongly stating an opinion by starting the sentence with "I". Believe is better in this case, because not only does the sentence starts with "我" but it also use the word "最好" instead of "很好" or if the person said "pretty good". The sentence would be structured differently if you were conveying a more polite "think" because the speaker would not use it with "best".
Nope. "Tasty" and "tastiest" are not words commonly used in the US to describe food or drink in this context. It's more natural to say "delicious", "good", or "the best." Some people might say: "that was really tasty!", but it's used more as a special compliment than a generic description.