Improve language filter (#5724)

* Scrub text of html before detecting language.

* Detect language on statuses coming from activitypub.

* Fix rubocop comments.

* Remove custom emoji from text before language detection

app/lib/activitypub/activity/create.rb

@@ -173,7 +173,7 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
   end
 
   def language_from_content
-    return nil unless language_map?
+    return LanguageDetector.instance.detect(text_from_content, @account) unless language_map?
     @object['contentMap'].keys.first
   end