How would it be possible, with as late a POD as feasible, to save the languages of Europe (other than the standard variants of the most prestigious languages) from decline or extinction? Languages such as, for example, Breton, Corsican and Occitan in France, Neapolitan, Lombard and Piedmontese in Italy, Basque, Catalan and Galician in Spain, and the Brythonic and Gaelic languages of Ireland and Great Britain. Making them official is not necessary, a situation of diglossia akin to that of the Arab countries or the German-speaking part of Switzerland would be enough.
I thought about this after realizing how, in the aforementioned Alpine country, the local dialects of German are alive and well, but those of French have been largely displaced by the standardized variety of the same language.