"I wear school uniform on Friday."

Translation: Dw i'n gwisgo gwisg ysgol dydd Gwener.

[Jonlang_]

Shouldn't this be Dw i'n gwisgo gwisg ysgol ar ddydd Gwener

or Dw i'n gwisgo gwisg ysgol ddydd Gwener ?

[EllisVaughan]

No since the "ar" has been lost it doesn't have to mutate. (it can but it doesn't have to).

[JFLB96]

Why does it lose the 'ar'? This is the first time I've been asked about 'on a day' so I included it and was told that I was wrong.

[EllisVaughan]

It should be accepted with the "ar" at least that's how I've always used it, but it is pretty common to drop it.

[Jonlang_]

ar causes soft mutation, so dydd becomes ddydd, because of this the ar can be dropped leaving the mutation to do the job of conveying "on".

[mirekfranc]

I put "Dydd Gwener dw i'n gwisgo gwisg ysgol." because I sometimes saw the day at the beginning of a sentence. Is that wrong? I'm a bit confused where the time should go.

[Jonlang_]

The time can go at the start or the end, like English. But in this sentence it's at the end.