"Do you want to go to the pub?"
Translation:Dych chi eisiau mynd i'r dafarn?
I agree. If anything, it should give you "i'r tafarn" as a correct answer, but call it a typo.
So, from what a I gather, when going to a named place like another town, or "chapel", you don't use the definitive, but otherwise you do translate and use the definite as it is.