@aloe
might be a confusion with something that happened to "k" rather than "i/u". Tolkien:
> But in one point of spelling Salesbury's influence was important. He gave up the use of the letter "k", which had in medieval Welsh been used more frequently than "c". Thus was established one of the visible characteristics of modern Welsh in contrast with English: the absence of "k", even before "e", "i", and "y". Students of English, familiar with the similar orthographic usage of Anglo-Saxon scribes derived from Ireland, often assume that there is a connexion between Welsh and ancient English spelling in this point. But there is in fact no direct connexion; and Salesbury, in answer to his critics (for the loss of "k" was not liked), replied: C for K, because the printers have not so many as the Welsh requireth. It was thus the English printers who were really responsible for spelling Kymri with a C.
I suppose it's possible this happened to the i/u too (Old Welsh used them rather than y/w). but I find that implausible because these are like, two out of five cardinal Latin vowels, and in the old days Latin was the primary printed language. I can't image a print shop having more y/w types than i/u. even if the English printers adapted their sets for English, that also has more i/u than y/w. but "k" is a Greek letter, not Latin, and originally used for loans only; so it makes sense that printers would have fewer of them than C's.
#Welsh