"I will wear white clothes on Sunday."
Translation:Gwisga i ddillad gwyn ddydd Sul.
I don't really understand why dydd is correct, when earlier we were taught than 'on' a day was translated as 'ddydd'. I now know that duo accepts, and indeed expects, both, but I can't see why...
The mutated form ddydd is better Welsh for 'on' a particular day, but it is not always taught to beginners for some reason, and it is not always used in casual Welsh.
Best to use it.
I thought saying I am going to was an acceptable way of saying I will - i.e. dw i'n mynd gwisgo...
The constructions are different in both English and in Welsh, so when you are learning it is useful to match them up:
- Dw i'n mynd i wisgo... - I am going to wear...
- Gwisga i... - I will wear