Get language from headers

[ngosang]

Issue details

Currently you are getting the language information from the "lang" tag, but many sites doesn't have this tag and uses HTTP headers instead.
My proposal is to use the "lang" tag and if it's not available get the language from the header "Content-Language".
Example URl without tag but with header:
http://www.investopedia.com/university/introduction-stock-trader-types/pivot-traders.asp

Environment

• wallabag 2.2.2

[tcitworld]

Please report this to Graby instead.

[tcitworld]

But thanks for the tip ;)