Translation:Yes I would
This seems to be a terribly irritating feature of the Welsh Duolingo that sometimes "yes" alone is not accepted as the translation of the various words that would perform that function, while here "yes" alone is required. I am happy to translate either way, but it shpild be consistent across the labguage program (I believe it is on the Irish program, for instance).
That is part of what the beta is for - to fill up such missing translation alternatives so that a more "rounded" experience develops across the sentences.
For what it's worth, when I looked at this sentence discussion, the "best" sentence was "Yes I would" (no comma or full stop, but not the single word "Yes", either).