"After Dewi Lingo went, I had a coffee."
Translation:Ar ôl i Dewi Lingo fynd, ges i goffi.
In the multiple choice question, both "ces i goffi" and "ges i goffi" are correct. Does this mean the mutation is optional in this case, and if so, why?
In positive statements traditionally there would be a "mi" particle coming before the verb which caused a soft mutation (it's still common in the north). Since the "mi" particle is left out the mutation becomes optional.
The base form (un-mutated) is used. I wouldn't recommend thinking about them as all acceptable spellings and instead grammatical variant of the original word. E.g gath, nghath, and chath would never be seen in a spelling test because they technically aren't words in their own right instead they're variants of Cath.