tl;dr

The new Natural Earth v4.1 populated places file now includes localized names in a name_*, specifically:

1. Expands the name localization added in v4.0 to 21 languages (up from 7) and several
   dozen themes expanding from populated places to include all admin-0, admin-1,
   rivers, lakes, playas, geographic lines, physical labels, parks, airports, ports, and
   more. As part of this work a new unique and stable "ne_id" has been added for any
   feature with a name translation &/or a Wikidata ID concordance. The full list of
   languages is:

name_ar,
name_bn,
name_de,
name_en,
name_es,
name_fr,
name_el,
name_hi,
name_hu,
name_id,
name_it,
name_ja,
name_ko,
name_nl,
name_pl,
name_pt,
name_ru,
name_sv,
name_tr,
name_vi, and
name_zh

(Names with * indicate
new language in v4.1 series.) A 2-character language code decoder ring is here:
https://en.wikipedia.org/wiki/List_of_ISO_639-2_codes. Props to Wikidata for their
CC0 license: https://www.wikidata.org/wiki/Wikidata:Introduction.

This is for many themes, not just populated places. So work here should be generic for many theme imports.

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Original title: Include OpenStreetMap language data for Natural Earth features

For example, ocean names are available in many languages at zooms 9 and higher, but only in English at zoom 8 and lower. Example map: https://mapzen.com/tangram/play/?scene=https%3A%2F%2Fapi.github.com%2Fgists%2F9f177672cdaac4640ea1b519cde3420d#9.4233/13.3585/-38.4174

If you zoom out below zoom 9, the label disappears.