"Dw i wedi mynd i'r parc heddiw."
Translation:I have gone to the park today.
Because that's incorrect English :P "I have gone" is the proper English :P
Eh, I'd say that the proper English is "I went to the park today"!
Using "have gone" together with "today" sounds odd to me.
Oh, yes, definitely! One of the course contributors thought that this sentence would be OK. It's clearly not, but there you go.
"Dwi wedi bod i'r parc (heddiw)" - I have been to the park (today) (using bod) "Dwi wedi mynd i'r parc" - I have gone to the park (using mynd)
That is actually bad English. You can't use the perfect tense when you add a time . You can say, I have been to the park, but when you add a time or day you must use the preterit: I went to the park today.
This was a bit of an experiment in the first course. From classroom experience I thought it would be useful to teach a very simple way of talking about past events while avoiding all the complications of Welsh such as mutations and an infinite number of ways of saying 'yes' and 'no'.
This wasn't popular with Duolingo users who, mostly, wanted to learn completely correct forms rather than an easy workaround and so to avoid the deluge of criticism it has been much reduced in the revised course.