Add user content translations with configurable backends (#19218)

app/serializers/rest/translation_serializer.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class REST::TranslationSerializer < ActiveModel::Serializer
+  attributes :content, :detected_source_language
+
+  def content
+    object.text
+  end
+end