Since Wycliffe was able to make a readable translation in 1400ish, and since some of the dialects had translations of some parts earlier, there was some capability. Tyndale was forced to choose between dialects as he translated, and his translation and the ones that followed in some ways created English by giving a standard text.
Or so I’ve read. I’m NOT a scholar of medieval english or anything that came before it!
The Dutch put up with the same nonsense. The big question here is why English didn't split up into a variety of true dialects in its conquest of the world, and that's probably because it has a standardized written language with the world's largest vocabulary suitable for any purpose ~