There is a good explanatory article on "Wikipedia" under the title "The treachery of the Blue Books".
Basically, the level of education across both England & Wales was very poor at this time (Scotland had its own, better, system.). A commission was sent to review Education in Wales : "The enquiry was carried out by three English commissioners, Ralph Lingen, 1st Baron Lingen, Jellynger C. Symons and H. R. Vaughan Johnson. The commissioners visited every part of Wales during 1846, collecting evidence and statistics. However, they spoke no Welsh and relied on information from witnesses, many of them Anglican clergymen at a time when Wales was a stronghold of nonconformism."
This is where "the imperialist Anglo-centric C19th zeitgeist." comes in. The commissioners could not, or would not, recognise that children educated in the non-conformist Sunday schools (which were real schools, teaching the basics) were both literate and numberate but in their own language, Welsh.. Had their report stopped there, it would have been bad enough but they went on to attack,without justification, the whole culture of Wales, attempting to connect Non-Conformity and the separate language with a whole raft of social ills. This was typical of the approach of English-speaking colonists in the Empire at this time, dismissing local cultures, denigrating anything seen as "different", and, in particular, trying to discourage the use of the native languages. The "Welsh Not" notices used to punish, embarrass and denigrate children heard speaking their own language in school was replicated certainly in Canada and New Zealand, (and probably other colonies) where pupils were often beaten for using the language of their home and community in school.
This policy seems to have worked in Ireland where, despite strenuous efforts after Independence, the language survives but has not revived. In Wales, retention of the language has always been seen as important to help define the nation and there is an understanding that "a people who lose their language lose their soul".
My Welsh forbears, unlike Pinot's, regrettably lost their language and I was not brought up in Wales so I have only a few words but, as an example of "lost in translation", try to explain all the connotations of "hiraeth" in one English word ! Impossible, there is no true English equivalent ! At times it can be very frustrating not to have the right words available to express a feeling in simple terms !
This is why I use "Yma o hyd" as a byline. It means "We are still here" and is just a gentle reminder that there people with older roots than the English in these islands and that, despite nearly a thousand years of attempting to assimilate them, they have retained their identity.
Maec