Fix youtube captions that disappeared with multi-language caption support

[BLD-889]

common/lib/xmodule/xmodule/video_module/video_module.py

@@ -245,21 +245,23 @@ class VideoModule(VideoFields, XModule):
             elif self.sub:
                 track_url = self.runtime.handler_url(self, 'transcript').rstrip('/?') + '/download'
 
-        if self.transcript_language in self.transcripts:
-            transcript_language = self.transcript_language
-        elif self.sub:
+        if not self.transcripts:
             transcript_language = 'en'
-        elif self.transcripts:
-            transcript_language = self.transcripts.keys()[0]
+            languages = {'en': 'English'}
         else:
-            # this for the case, when for currently selected video,
-            # there are no translations and English subtitles are not set by instructor.
-            transcript_language = 'null'
+            if self.transcript_language in self.transcripts:
+                transcript_language = self.transcript_language
+            else:
+                transcript_language = self.transcripts.keys()[0]
 
-        all_languages = {i[0]: i[1] for i in settings.ALL_LANGUAGES}
-        languages = {lang: all_languages[lang] for lang in self.transcripts}
-        if self.sub:
-            languages.update({'en': 'English'})
+            languages = {
+                lang: display
+                for lang, display in settings.ALL_LANGUAGES
+                if lang in self.transcripts
+            }
+
+            if self.sub:
+                languages['en'] = 'English'
 
         # OrderedDict for easy testing of rendered context in tests
         transcript_languages = OrderedDict(sorted(languages.items(), key=itemgetter(1)))