feat: Localised urls/slugs for static pages

Summary

Currently, paths for html pages are defined by the filename, or overwritten by frontmatter. With I18n, it would be quite useful to be able to localise this. This is partly SEO and partly general user friendly urls for non-English speakers.

Motivation

Additional flexibility in I18n routing.

Reference-level explanation

This is a feature that is supported in middleman: https://middlemanapp.com/advanced/localization/#localizing-paths

Essentially, you can use I18n keys to alter the slug on a per-locale basis. E.g. /en/hello maps to /es/hola

I'm not sure how best to implement this in the core, but I was able to write a small plugin that demonstrates the functionality. This has a couple issues, such as not interacting with the existing I18n route logic, and not always reloading right in development mode, but it works well enough.

class Builders::I18nSlug < SiteBuilder
  def build
    generator do
      # raise site.collections.pages.resources.inspect
      site.collections.pages.resources.each do |resource|
        path = translated_path(resource)
        resource.data['permalink'] = "#{locale_prefix(resource)}/#{path}.html" if path
      end
    end
  end

  private

  def translated_path(resource)
    key = resource.data.slug_key
    I18n.with_locale(resource.data.locale) { I18n.t(key, scope: 'paths', default: nil) }
  end

  def locale_prefix(resource)
    prefix = ''
    if resource.data.locale != config.default_locale || config.prefix_default_locale
      prefix << "/#{resource.data.locale}"
    end
    prefix
  end
end

bridgetownrb / bridgetown