Are nation-states necessary to preserve cultures and languages?

Branko Milanovic has written an excellent post on the trade-off between global equality and the preservation of cultures, traditions and languages that results form the preservation of "countries". The argument is that if we allowed free migrations, global income equality would increase but some small countries would de facto disappear because a majority of the population would abandon them. But then some traditions, cultures and languages that are preserved by these countries would disappear. If we accept that this disappearance would have such a cost, then we have to integrate this cost in the social evaluation of a policy of free migration. I agree that losing cultures, languages and traditions has an enormous social cost, as well as the extinction of animal species is a cost for nature and the environment. However, I would question the principle that nation-states ("countries") are necessary to preserve languages, cultures and traditions. Actually, nation-states have been as effective preserving languages as destroying them, as only a few nation-states have been able to promote the linguistic diversity that characterizes most of them (certainly not Spain under Franco). The pattern of one country, one flag, one language, one culture, one army, one currency, is something that hardly exists anywhere in the world (certainly not in Europe). I also feel uncomfortable with the practice of associating one language with one national flag, which is quite common in the Internet. What is the flag of the Spanish language, spoken in so many countries? What is the flag of the English language, spoken as a first language in many countries and as a second language in many more? Even my own mother language, Catalan, is not only spoken in the administrative autonomic region of Catalonia, but also in other Spanish territories, as well as in regions of France or Italy. Is there any language whose borders coincide with a nation-state? Perhaps yes, but none comes to my mind. If we are serious about protecting language and cultures, these should be preserved by good federal international and local institutions that have as objective the preservation and promotion of most of them if not all (at a reasonable cost), and not the conflict between them. There are more than 4000 languages in the world, and we cannot have one country for each of them, but they are part of the cultural wealth of all humanity. I would like Catalan to be one of the great European languages, and this can only be achieved by a multi-institutional effort with the cooperation of agents from several territories.