Personally I don't think much of their instructions anyway. .... they seems to assume too much and too little. They don't bother to point out which end of the toothbrush you should hold on to for a start. What do you do if you do swallow?.. Is it a 999 job or what?... how far from "pea-sized" are you allowed to stray, and does it depend on your size?... do people with huge buck teeth need to use more, and if so, how much more? What will happen if you only brush once a day? What do they mean by "thoroughly"?
Anyway, as they luckily haven't done the Welsh version, you can do it.
You can do it seriously ,thoroughly, briefly, humourously, officiously, oddly, wrongly, misguidedly, dangerously, goofily, gloomily, misleadingly, reassuringly, prettily, off-handedly, bullet-pointedly,sexily, sergeant-majorishly .... as long as you get to use plenty of Welsh and learn stuff from it. Yes, I know you've got 88 years, but we still need to press on, because between you and me, 88 years is bit on the optimistic side.