English phrases in Welsh dialogue

Following on at a slight tangent from my previous question re Anglicisms, I have noticed in Welsh novels I have been reading that whenever you get a character who lards his or her (usually her) speech with a lot of actual English, as distinct from Welsh anglicisms, it is a sure sign that the character is trying to sound posh and is in fact to be taken as sounding ridiculously affected. For example: ‘A ’fedra’ i ddim, on my conscience, roi hundred pounds Anti Edith druan i’r capel os ydi o i fod yn lle i bobol fel yr hen Tom Tom ’na. I just can’t do it, ydach chi’n dallt.’ (from ‘O Law i Law’). I guess the equivalent in an English novel would be a character who felt that using French phrases added a certain je ne sais quoi to the discourse, n’est-ce pas?
I don’t know whether this is a just a novelistic convention or if that kind of thing would still come across as pretentious/ridiculous in reality?

Wouldn’t it be the Boris Johnson use of Latin phrases type person, showing that they went to Public School and had a Classical Education? I am not sure how ‘wiffwaff’ for table tennis fits with that!

Bit of a movable feast - ‘O Law i Law’ is going back a bit, when it would have been a much more common perception that speaking English was trying to show off - now, it’s so deeply and widely normalised that this wouldn’t be the most immediate thought/expectation - but having said that, you will still hear people (usually older) using English words in a kind of ever-so-faintly ironic ‘aren’t I being posh’ kind of way - particularly ‘thank you’, oddly enough…