When did encumbrance translate into pounds?
That's never been stated. In the games, the weight units used for encumbrance are never named. While I can understand one assuming they translate into pounds (Or any other real weight limit, for that matter. But a sword weighing 20 kilograms makes even less sense.) since if not told otherwise, you might naturally equate an unspecified unit of anything with one you're familiar with, that really doesn't have to be the case. Though that doesn't mean we can't question whether the item weights make sense, just that unless we're ever told that one unit of encumbrance is one pound, we shouldn't judge them based on the assumption that items are weighted in pounds. Rather, what we should do is look at the reletive weights of items. Because while we don't know how much an Elder Scrolls encumbrance unit is, we woulsd logically assume that if we take an item which exists in our every day life, say, a carrot, in the Elder Scrolls it should have roughly the same weight as a real life carrot. Now that we have the carrot, we can compare it to a sword, how many carrots does it take to get the same amount of weight as the sword in the game? Now, how many carrots would it take to balance out the weight of a real life sword of similar design and material? If there's a significant difference, then it probably means that the weight of the sword in the game isn't realistic.
But I didn't see any mention of the weight of weapons in the game not being accurate, if we assume that weight in the game is rendered in pounds. It seems that the main issue here is a misconception on the part of forum posters, using the notion that swords are heavy, unwieldly weapons as an argument on which to base how melee combat should work. Myself, I'm not an expert on the matter, but if people who actually took the time to research the matter are saying that the OP is correct, I'm not going to disagree with them. It seems logical to me that swords wouldn't be as heavy as some people seem to assume they are too, because you have to not only carry you're weapon, you have to swing it too, and carrying heavy objects is tiring, swinging them around is even more so, thus, logically, you'd want you're weapon to be light enough and well balanced enough to be practical to use. So in conclusion, swords aren't as heavy as people seem to assume they are. But how much bearing that has on the game is uncertain, since Bethesda is probably more concerned with fun and game balance than accurately simulating real life sword play. So evwn if they took the time to research the weight of historical swords, they may choose not to reflect this in the game.
Wikipedia has less mistakes then the Encyclopedia Brittanica.
That's not something I'd know about it, but I'd certainly put far, FAR more stock in any given article I read on it than forum posts by random people who provide absolutely no source for their information and don't support their supposed "facts" with any real evidence.
It seems to me that there's a disturbingly common trend to assume that any information found on Wikipedia is automatically wrong, even though I actually can't think of any case where I've found information on Wikipedia that I know to be wrong, I've seen articles which don't give enough information, certainly, but I can't remember having experiences with blatently wrong articles. Now, certainly Wikipedia shouldn't be used for serious academic research, but that's far from what we're doing here, all we're doing is discussing an upcoming fantasy game.