Canonicalise per locale and declare hreflang alternates

German content is reachable at both /updates/foo and /de/updates/foo,
and a page with no English translation renders German at
/en/updates/foo through the fallback chain, so three URLs each
claimed to be canonical. Both tags now derive from one
locale-to-URL function, which points every duplicate at the address of
the version actually served, the unprefixed German URL, matching
default_url_options.

Alternates are declared only for locales in which the page genuinely has
a translation, since /en/ serving German through the fallback is not an
English version of the page. x-default points at German, the site's
primary language.

1 files changed, 7 insertions, 0 deletions

diff --git a/app/views/layouts/_social_meta.html.erb b/app/views/layouts/_social_meta.html.erb
index 9a86d26d..36547d26 100644
--- a/app/views/layouts/_social_meta.html.erb
+++ b/app/views/layouts/_social_meta.html.erb
@@ -23,6 +23,13 @@
     <meta property="og:locale:alternate" content="<%= alternate %>"/>
   <% end %>
 
+  <% if (hreflang_alternates = og_hreflang_alternates).any? %>
+    <% hreflang_alternates.each do |code, url| %>
+      <link rel="alternate" hreflang="<%= code %>" href="<%= url %>"/>
+    <% end %>
+    <link rel="alternate" hreflang="x-default" href="<%= og_locale_url(I18n.default_locale) %>"/>
+  <% end %>
+
   <% if og_published_time %>
     <meta property="article:published_time" content="<%= og_published_time %>"/>
   <% end %>