Serialize language into ActivityPub JSON (#7840)

* Serialize language into ActivityPub JSON

* Only use contentMap if language is present

app/serializers/activitypub/note_serializer.rb

@@ -1,12 +1,15 @@
 # frozen_string_literal: true
 
 class ActivityPub::NoteSerializer < ActiveModel::Serializer
-  attributes :id, :type, :summary, :content,
+  attributes :id, :type, :summary,
              :in_reply_to, :published, :url,
              :attributed_to, :to, :cc, :sensitive,
              :atom_uri, :in_reply_to_atom_uri,
              :conversation
 
+  attribute :content, unless: :language?
+  attribute :content_map, if: :language?
+
   has_many :media_attachments, key: :attachment
   has_many :virtual_tags, key: :tag
 
@@ -26,6 +29,14 @@ class ActivityPub::NoteSerializer < ActiveModel::Serializer
     Formatter.instance.format(object)
   end
 
+  def content_map
+    { object.language => Formatter.instance.format(object) }
+  end
+
+  def language?
+    object.language.present?
+  end
+
   def in_reply_to
     return unless object.reply? && !object.thread.nil?