[vlive] Use locale as subtitles language key instead
diff --git a/youtube_dl/extractor/vlive.py b/youtube_dl/extractor/vlive.py
index 8d671cca767..c3aa57cd6fe 100644
--- a/youtube_dl/extractor/vlive.py
+++ b/youtube_dl/extractor/vlive.py
@@ -116,7 +116,7 @@ def _replay(self, video_id, webpage, long_video_id, key):
 
         subtitles = {}
         for caption in playinfo.get('captions', {}).get('list', []):
-            lang = dict_get(caption, ('language', 'locale', 'country', 'label'))
+            lang = dict_get(caption, ('locale', 'language', 'country', 'label'))
             if lang and caption.get('source'):
                 subtitles[lang] = [{
                     'ext': 'vtt',

## Please follow the guide below
### Before submitting a *pull request* make sure you have:
- [x] At least skimmed through [adding new extractor tutorial](https://github.com/rg3/youtube-dl#adding-support-for-a-new-site) and [youtube-dl coding conventions](https://github.com/rg3/youtube-dl#youtube-dl-coding-conventions) sections
- [x] [Searched](https://github.com/rg3/youtube-dl/search?q=is%3Apr&type=Issues) the bugtracker for similar pull requests

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### What is the purpose of your *pull request*?
- [ ] Bug fix
- [x] Improvement
- [ ] New extractor
- [ ] New feature

---

The extractor was using language e.g. ``zh`` as the subtitle language, this doesn't distinguish between variants like ``zh_CN`` and ``zh_TW``.

```
$ # Before
$ python -m youtube_dl --list-subs "http://www.vlive.tv/video/16937"
[vlive] 16937: Downloading webpage
[vlive] 16937: Downloading JSON metadata
Available subtitles for 16937:
Language formats
el       vtt
en       vtt
zh       vtt
pt       vtt
vi       vtt
ko       vtt
th       vtt
in       vtt
ja       vtt
es       vtt

$ # After
$ python -m youtube_dl --list-subs "http://www.vlive.tv/video/16937"
[vlive] 16937: Downloading webpage
[vlive] 16937: Downloading JSON metadata
Available subtitles for 16937:
Language formats
th_TH    vtt
ko_KR    vtt
pt_BR    vtt
zh_CN    vtt
zh_TW    vtt
vi_VN    vtt
ja_JP    vtt
en_US    vtt
el_GR    vtt
es_ES    vtt
in_ID    vtt
```

