UI chrome should be localizable

[1ec5]

Virtually all of the content in the Americana application is localizable, and much of it is already translated. However, major parts of the UI are still hard-coded in English:

• GL JS controls¹
• Samples and Legend buttons
• Map attribution²
• Language switcher
• Legend entries (other than the “Route markers” section)
• “Fork me on GitHub”
• Search box

To the extent that we need to maintain our own translation tables, there’s an implementation in #215 (comment) that we can lift pretty easily. For the time being, I don’t think we’ll have enough translatable strings to require a translation management system such as Transifex or Translatewiki.net, but that can happen after we have basic infrastructure in place for translations.

Footnotes

1. When configuring the map, we can set the locale option to provide our own translations of these strings. Unfortunately, GL JS doesn’t provide translations of its own: https://github.com/mapbox/mapbox-gl-js/issues/12109#issuecomment-1195748154. ↩

2. Ideally, the metadata associated with each tileset would come with localized attribution strings, just as the tilesets provide localized versions of each feature’s name. However, the TileJSON format only supports a very basic format for attribution: Structured attribution mapbox/tilejson-spec#20. ↩