I don't understand what's so bad about admitting that people may use and understand the same words in slightly different ways.
Suppose there is a community of Martians who have a word for true justified belief, but no word for knowledge. When these Martians learn English, they might at first take "knowledge" to be synonymous with their word: the difference hardly shows up in ordinary contexts. So when they use "knowledge", they mean true justified belief.
This clearly seems possible. And it seems just as possible that it could happen with people from East Asia rather than from Mars. What kind of evidence would confirm that it really does happen with East Asians? Well, for instance, evidence showing that they systematically classify Gettier cases as "knowledge".
The actual evidence doesn't look quite like that. It rather suggests that East Asians use "knowledge" for something complicated which is however not exactly what we (Western, high SES philosophers) use it for. The evidence also suggests that there is considerable disagreement even within the East Asian population about the classification of Gettier cases. Which suggests that East Asians don't all mean the same by "knowledge".
I say "suggests" because the data doesn't show that the disagreement couldn't be resolved by either providing more information about the Gettier cases or by giving the subjects more time to think about them. I also think the results would have been quite different, and less interesting, if the subjects were offered more than just two options. Perhaps I'll say more on this later. For now let's assume that all this is not so. What are we to make of this?
I don't know whether it shows that East Asians do not share our concept of knowledge. For I don't know what sharing a concept involves. I'm usually at a loss when philosophers start talking about concepts. I also don't want to claim that the word "knowledge" has a different meaning for East Asians and us. Whether that's true depends on what theoretical role we assign to "meaning". There probably are good reasons in various semantic projects to say that there is only one common meaning of "knowledge" in English. (The common meaning is then presumably not fully determinate: it leaves Gettier cases undetermined.) What I mean when I say that we mean slightly different things by "knowledge", is only that we disagree about the conditions under which (English) sentences containg "knowledge" are true.
Weinberg, Nichols and Stich argue that this creates a problem for epistemology:
If [people mean different things by "knowledge"], then the arguments for skepticism in the philosophical tradition pose a serious challenge to the possibility of having what Hight SES, white Westerners with lots of philosophical training call 'knowledge'. But those arguments give us no reason to think that we can't have what other people [...] would call 'knowledge'.
Sure. Skeptical arguments don't undermine the possibility of having, say, true beliefs, or strawberries. So if other people call true beliefs "knowledge", or strawberries, then skeptical arguments don't undermine the possibility of having what these people call "knowledge". So what? Nobody in their right mind ever thought an argument could show that "we don't have knowledge" is false on any possible interpretation of that sentence. Weinberg, Nichols and Stich continue:
And, of course, those skeptical arguments give us no reason at all to think that what High SES white Western philosophers call 'knowledge' is any better, or more important, or more desirable, or more useful than what these other folks call 'knowledge' [...]. Without some reaon to think that what white, Western, High SES philosophers call 'knowledge' is any more valuable, desirable, or useful than any of the commodities that other groups call 'knowledge', it is hard to see why we should care if we can't have it.
So assume strawberries are more valuable, desirable and useful than knowledge. Does it follow that we shouldn't care if we can't have knowledge? Obviously not. I don't see how this argument is even supposed to work. If other people mean other things by "knowledge", then the value and importance of what they mean should be independent of and irrelevant to the value and importance of what we mean by "knowledge".
In the case of epistemology, I actually think the word "knowledge" is dispensable. What we really care about is true belief. The skeptical worry is that there are reasons undermining our confidence in the truth of certain rather trivial beliefs: Can we really be sure that we have hands, given that all our evidence doesn't rule out that we are brains in vats? Are there any non-question-begging reasons to believe that we are not brains in vats? No need to mention knowledge at all.
But anyway, suppose knowledge (that is, what we Western, High-SES philosophers mean by "knowledge") really plays a central role in epistemology. Does it matter if other people lack a word for it, and use "knowledge" for something else? I don't think so. Why should it? Supervenience plays an important role in metaphysics despite the fact that most people don't have a word for it.
It would admittedly be a little disturbing if people who use "knowledge" for something else found what we call "knowledge", after having learned what that is, unimportant and useless. But firstly, there is no evidence at all that this is the case. And secondly, it would only show that people's interests and values are more different than we might have expected. The fact that some people find freedom and democracy unimportant and useless hardly shows that they really are, or that we also shouldn't care about them.