Very true, and thanks for giving us the correct way to say 'went', but I'm afraid I disagree about changing the tense in the translation making the answer wrong. It may work in Welsh (I don't know the language well enough to know, but I'm going to assume they're giving us the correct grammar), but the present perfect tense doesn't work like that in English for correct grammar. You can't have a specific time and use present perfect. The tense is used to refer to an action that took place in the past at an unspecified point in time. 'I have gone to the park (at some point before now). I went to the park yesterday.'
Which isn't to say I'd never say the sentence 'I have gone to the park yesterday', but probably only when I'm telling someone a story and want to sequence the order events took place (I have gotten up, I've gone to the park, and suddenly I see a bear!). Without context, I think they should allow the English to translate to 'went' and 'have gone' when a specific time is mentioned.
I agree - the point is that the 'same' tense in termns of grammatical construction may be used in different ways in different languages, so "I have gone to the park yesterday" is definitely incorrect English, which means that it is not the correct translation into English. I have been teaching English overseas for 20 years, and would always correct any student of mine who came up with such a sentence, explaining the reason mentioned by eirlana. This point is so fundamental in the tenses used in English, that even if we don't specify exactly when something happened, we still switch to past simple when giving more details about an experience, e.g. " Yes, I have been to New York. I went with my family. We spent 2 weeks there. We stayed in a hotel near Times Square. We visited the Empire State building. We ate in a diner." Note that all these sentences in past simple would sound unnatural in present perfect because, even though we haven't specified when the trip to NYC was, we still kow that these actions occurred in the specific past time period of 'When I was in New York". Also, the guidelines given here state that natural sounding translation is preferred: https://www.duolingo.com/comment/924931