"Monday I make breakfast."
Translation:Dydd Llun dw i'n gwneud brecwast.
I believe "dydd Llun" mutates to "Ddydd Llun" when used as a prepositional phrase.
It would if the preposition "ar" was used before it (i.e. "Ar ddydd Llun"), but not otherwise (mutations are about what comes before). TBH I'm not sure that leaving out the "ar" and using "Dydd Llun" as a preposition is particularly good Welsh, but I'm a bit rusty
The way my current instructor tells it, you mutate "Dydd" in this context, even without the "ar". (It might be that the "ar" is implied.) Like, if spoke this sentence without the mutation, he'd correct me.
Hmm, interesting. It's quite possible that they're right - I learnt natively as a child so I don't really know any of the rules, just what things should sound like, and saying "ddydd" without anything in front of it sounds weird to me. Either way, you definitely wouldn't be corrected for it in normal speech!
And that's the trick with Welsh. There seems to be a very descriptivist attitude towards the language - which is awesome! But makes it difficult to flag a usage as "wrong". One of my axioms is "Somewhere, there's a village where this is correct."