YouTube has closed captions url for each language

[sebaro]

Checklist

• I'm reporting a broken site support issue
• I've verified that I'm running youtube-dl version 2020.03.08
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

[youtube] fJ9rUzIMcZQ: Looking for automatic captions
[info] Writing video subtitles to: Queen – Bohemian Rhapsody (Official Video Remastered)-fJ9rUzIMcZQ.ro.vtt
send: b'GET /api/timedtext?v=fJ9rUzIMcZQ&xorp=true&hl=en&ip=0.0.0.0&ipbits=0&expire=1583947243&sparams=ip%2Cipbits%2Cexpire%2Cv%2Cxorp&signature=31A25893551B51525DE37B94CA9536A7583485DD.415413D23C633FEFAB036FA9C96C0F1DB7C2FECD&key=yt8&lang=ar&tlang=ro&fmt=vtt HTTP/1.1\r\nHost: www.youtube.com\r\nCookie: PREF=f1=50000000&hl=en; s_gl=1d69aac621b2f9c0a25dade722d6e24bcwIAAABVUw==; YSC=gGwmULRgjnE; VISITOR_INFO1_LIVE=rkNlx8Rw4LU\r\nUser-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3667.1 Safari/537.36\r\nAccept-Charset: ISO-8859-1,utf-8;q=0.7,;q=0.7\r\nAccept: text/html,application/xhtml+xml,application/xml;q=0.9,/*;q=0.8\r\nAccept-Encoding: gzip, deflate\r\nAccept-Language: en-us,en;q=0.5\r\nConnection: close\r\n\r\n'
reply: 'HTTP/1.1 200 OK\r\n'

Description

YouTube now has an cc url for each language:

"captionTracks":[{"baseUrl":"https://www.youtube.com/api/timedtext?v=fJ9rUzIMcZQ\u0026xorp=true\u0026hl=en\u0026ip=0.0.0.0\u0026ipbits=0\u0026expire=1583948462\u0026sparams=ip,ipbits,expire,v,xorp\u0026signature=72B2059E51E420A1D99DB46F7019E78087406721.536C4092C7C97466EF1B463F0D3AA8C6EDB12458\u0026key=yt8\u0026lang=ar","name":{"simpleText":"Arabic"},"vssId":".ar","languageCode":"ar","rtl":true,"isTranslatable":true},{"baseUrl":"https://www.youtube.com/api/timedtext?v=fJ9rUzIMcZQ\u0026xorp=true\u0026hl=en\u0026ip=0.0.0.0\u0026ipbits=0\u0026expire=1583948462\u0026sparams=ip,ipbits,expire,v,xorp\u0026signature=72B2059E51E420A1D99DB46F7019E78087406721.536C4092C7C97466EF1B463F0D3AA8C6EDB12458\u0026key=yt8\u0026lang=zh-Hans","name":{"simpleText":"Chinese (Simplified)"},"vssId":".zh-Hans","languageCode":"zh-Hans","isTranslatable":true},{"baseUrl":"https://www.youtube.com/api/timedtext?v=fJ9rUzIMcZQ\u0026xorp=true\u0026hl=en\u0026ip=0.0.0.0\u0026ipbits=0\u0026expire=1583948462\u0026sparams=ip,ipbits,expire,v,xorp\u0026signature=72B2059E51E420A1D99DB46F7019E78087406721.536C4092C7C97466EF1B463F0D3AA8C6EDB12458\u0026key=yt8\u0026lang=zh-Hant","name":{"simpleText":"Chinese (Traditional)"},"vssId":".zh-Hant","languageCode":"zh-Hant","isTranslatable":true},{"baseUrl":"https://www.youtube.com/api/timedtext?v=fJ9rUzIMcZQ\u0026xorp=true\u0026hl=en\u0026ip=0.0.0.0\u0026ipbits=0\u0026expire=1583948462\u0026sparams=ip,ipbits,expire,v,xorp\u0026signature=72B2059E51E420A1D99DB46F7019E78087406721.536C4092C7C97466EF1B463F0D3AA8C6EDB12458\u0026key=yt8\u0026lang=cs","name":{"simpleText":"Czech"},"vssId":".cs","languageCode":"cs","isTranslatable":true},{"baseUrl":"https://www.youtube.com/api/timedtext?

Appending "tlang=" will translate from the language in the first cc url (Arabic) into the language from "--sub-lang" argument.

lang=ar&tlang=ro