Add language detection (#1772)

* Add language detection via WhatLanguage and (de)serialization of it through Atom

* Fix default language in ProcessFeedService

* Re-add newline before 'react-rails' Gem to fix groupings

Fixes Code Climate issue

app/lib/atom_serializer.rb

@@ -327,8 +327,8 @@ class AtomSerializer
   end
 
   def serialize_status_attributes(entry, status)
-    append_element(entry, 'summary', status.spoiler_text) if status.spoiler_text?
-    append_element(entry, 'content', Formatter.instance.format(status.proper).to_str, type: 'html')
+    append_element(entry, 'summary', status.spoiler_text, 'xml:lang': status.language) if status.spoiler_text?
+    append_element(entry, 'content', Formatter.instance.format(status.proper).to_str, type: 'html', 'xml:lang': status.language)
 
     status.mentions.each do |mentioned|
       append_element(entry, 'link', nil, rel: :mentioned, 'ostatus:object-type': TagManager::TYPES[:person], href: TagManager.instance.uri_for(mentioned.account))

app/services/post_status_service.rb

@@ -19,6 +19,7 @@ class PostStatusService < BaseService
                                       sensitive: options[:sensitive],
                                       spoiler_text: options[:spoiler_text] || '',
                                       visibility: options[:visibility],
+                                      language: detect_language(text),
                                       application: options[:application])
 
     attach_media(status, media)
@@ -51,6 +52,10 @@ class PostStatusService < BaseService
     media.update(status_id: status.id)
   end
 
+  def detect_language(text)
+    WhatLanguage.new(:all).language_iso(text)
+  end
+
   def process_mentions_service
     @process_mentions_service ||= ProcessMentionsService.new
   end

app/services/process_feed_service.rb

@@ -119,6 +119,7 @@ class ProcessFeedService < BaseService
         spoiler_text: content_warning(entry),
         created_at: published(entry),
         reply: thread?(entry),
+        language: content_language(entry),
         visibility: visibility_scope(entry)
       )
 
@@ -238,6 +239,10 @@ class ProcessFeedService < BaseService
       xml.at_xpath('./xmlns:content', xmlns: TagManager::XMLNS).content
     end
 
+    def content_language(xml = @xml)
+      xml.at_xpath('./xmlns:content', xmlns: TagManager::XMLNS)['xml:lang']&.presence || 'en'
+    end
+
     def content_warning(xml = @xml)
       xml.at_xpath('./xmlns:summary', xmlns: TagManager::XMLNS)&.content || ''
     end