Translation:Dy gar di.
I don't see why they shouldn't be accepted. But adding chi/di isn't colloquial in the sense of "slangy"; it's actually leaving it off that can be formal. The tendency to add chi/di is so strong that some would even say car chi - although that's extremely colloquial, and most likely won't be accepted. https://en.wikipedia.org/wiki/Welsh_language#Pronoun_doubling