I've been pondering the whole question of language death again today. This seems to me like a very interesting fault-line between my own outlook and the outlook of many opponents of leftism, liberalism, and political correctness; the Alt Right, the Alt Light, classical liberals, cultural libertarians, etc.
A frequent argument made against cultural relativism, and in favour of the West (and especially in favour of American exceptionalism) is: "Well, if we're so bad, why does everybody want to come here? If these other cultures are so great, why are so many people eager to leave them?"
I sympathise with this argument as a way of shutting up liberals. However, it troubles me in a broader sense. I don't think we should worship success.
When you apply this attitude towards language death we see how grim it really is. Presumably, lamenting language decline and language death is "linguistic relativism"; the best languages succeed and the lesser languages die; people vote with their tongues. I think few people would really want to follow this line of logic through when it comes to languages. I think the same perspective could be applied to cultures and traditions.
Personally, I have mixed feelings about success as a measure of how good or bad an institution is. In some ways, success-- especially over time- seems to be a sign that something is healthy and admirable. For instance, progressives lament ideals of masculinity and femininity, nationhood, and family life, but they are enormously and enduring popular. They are also good. (Of course, I am judging this by my own set of values.)
Perhaps time is the critical element. Anything that maintains its popularity over generations must surely have merit. The problem is that, if it loses its popularity in a single generation, it can be lost forever, or at least it can be extremely difficult to revive it. I think this is one of the insights that separates traditionalist conservatism from libertarianism.