Replying to myself to add that that last ~10% is an enormous time-sink. You'll have to look up every unfamiliar word, which isn't a big deal for a short text, but becomes one for something longer. Worse, though, is that you'll constantly be led astray by words whose meanings have drifted over time: your interpretation (often) won't align exactly with that of Chaucer or his audience. What I said above is good enough for casual / undergraduate use - the stories are still funny, and / or have enough depth for a good discussion - but there's a reason "medievalist" is an actual speciality: you'll spend a whole career trying to get to 100%.