I wrote "This is not tasty to me, this is bitter" and my answer was accepted, so I think they've now changed it. However in English (British) I would never say "This is not tasty to me" so I didn't expect my answer to be correct, I just couldn't come up with an alternative.
My conclusion is that in this situation Hebrew is more polite than English and the "to me" should be excluded in the English translation. If I was choosing to express my opinion in English rather than make a statement I would say "That tastes bitter to me". In English you need a verb if you are saying the words "to me".
This is an instance where a literal translation really doesn't work in English. Saying "This is not to my taste", while correct, is hopelessly formal. Saying "This is not tasty" is missing the point of including לי. The most natural phrasing in English is just "I don't like this. It is bitter." That doesn't contain the word "taste", but your not liking the taste is obvious from context. (But it isn't accepted.)
to me. To us: lanu,etc. Lamed means "to". The לי, לה, לו, לך להם, להן, לכם... All "to" + pronoun. To me, to her, to him, etc. This is all in the tips and notes, if you don't have them because you're in the app you can find them on the website, or search on discussions. Or just let me know I'll repost the links
The Hebrew sentence is making a subjective assessment. Literally, the speaker is saying "This isn't tasty TO ME. It is bitter." It's something you might say when tasting 80% dark chocolate, while acknowledging that your friend loves the stuff. (FWIW, I like 70% chocolate, but anything stronger is too bitter for me.)
The English sentence doesn't say "to me", so it claims to be an objective statement. The food isn't tasty, period. It's too bitter. If somebody else tastes it, they won't like it either.
Bottom line: Both the Hebrew and the English are plausible sentences, but they don't mean the same thing.