Use Wikidata as fallback source for language names

[claysmalley]

This is fine as a start, but maybe we could try to source the names dynamically from Wikidata, like we do for route networks in the legend. That would allow us to support more interface languages than just English, which seems appropriate for a feature focused on multilingualism.

Originally posted by @1ec5 in #1186 (comment)

In the language picker, Americana sources language names from CLDR. Many languages are missing names in CLDR, including hundreds of indigenous languages of North America. As a result, these languages are labeled as their 2- or 3-letter ISO 639 code, which makes them hard to recognize and search for.

#1186 includes a fallback English name for each of the languages it introduces support for, but this is not a fully multilingual solution. Sourcing language names from Wikidata would improve multilingual support and make it easier for the general public to contribute translations.