FIX: Include some of the post content when detecting the title language (#277)

This commit appends some of the first post's text to the topic title when detecting the language. This modification does not affect the text that is sent for actual translation.

Author: nattsw

app/services/discourse_translator/base.rb

@@ -123,7 +123,16 @@ def self.translate_supported?(detected_lang, target_lang)
     private
 
     def self.text_for_detection(translatable)
-      get_untranslated(translatable, raw: true).truncate(DETECTION_CHAR_LIMIT, omission: nil)
+      text = get_untranslated(translatable, raw: true)
+
+      if translatable.class.name == "Topic"
+        # due to topics having short titles,
+        # we need to add the first post to the detection text
+        first_post = get_untranslated(translatable.first_post, raw: true)
+        text = text + " " + first_post if first_post
+      end
+
+      text.truncate(DETECTION_CHAR_LIMIT, omission: nil)
     end
 
     def self.text_for_translation(translatable, raw: false)

spec/services/base_spec.rb

@@ -34,7 +34,8 @@ class EmptyTranslator < DiscourseTranslator::Base
   end
 
   describe ".text_for_detection" do
-    fab!(:post)
+    fab!(:topic) { Fabricate(:topic, title: "it is a fine day") }
+    fab!(:post) { Fabricate(:post, topic:) }
 
     it "truncates to DETECTION_CHAR_LIMIT of 1000" do
       post.raw = "a" * 1001
@@ -46,6 +47,12 @@ class EmptyTranslator < DiscourseTranslator::Base
       post.raw = text
       expect(DiscourseTranslator::Base.text_for_detection(post)).to eq(text)
     end
+
+    it "appends some text from the first post for topics" do
+      topic.first_post.raw = "a" * 999
+      expected = (topic.title + " " + topic.first_post.raw).truncate(1000)
+      expect(DiscourseTranslator::Base.text_for_detection(topic)).to eq(expected)
+    end
   end
 
   describe ".text_for_translation" do