[youtube] Always request webpage in English (Fixes #3844)

youtube_dl/extractor/youtube.py

@@ -655,7 +655,9 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
 
         # Get video webpage
         url = proto + '://www.youtube.com/watch?v=%s&gl=US&hl=en&has_verified=1' % video_id
-        video_webpage = self._download_webpage(url, video_id)
+        req = compat_urllib_request.Request(url)
+        req.add_header('Cookie', 'PREF=hl=en')
+        video_webpage = self._download_webpage(req, video_id)
 
         # Attempt to extract SWF player URL
         mobj = re.search(r'swfConfig.*?"(https?:\\/\\/.*?watch.*?-.*?\.swf)"', video_webpage)