Apparently close to three-quarters of the inhabitants of Wales don't speak Welsh at all. Around 20% speak Welsh fluently (it is the least endangered of the surviving Celtic languages). Nearly all of them can also speak English.
I've never been to Wales, or to New South Wales for that matter.
As many people know, the Gaelic "Mac" means "son of" and is found in many surnames--McAllister, MacArthur, McDonald, etc. In some cases the ancestor from which the family takes its name is a known individual (like the ancestor of Clan Donald, the McDonalds).
In Welsh the corresponding word is Ap and that often appears as a P- at the start of a surname, like the Pritchard in the story (son of Richard), Powell (son of Howell), Pulliam (son of William), etc.