Hint: Language detection is in helpcontent2/help3xsl/index2.html
Note: Works in Firefox.
Already confirmed in Redmine -> NEW
Just out of curiosity:
1.What do we get when navigator.language is referenced?
According to the document written in Japanese below
(translation by me)
>Chrome 49.0.2623.75, as of 2016-03-07
>navigator.languages returned the same value as Accept-Language header.
>navigator.language returned the browser's UI Language.
the document may be outdated. It's more than three years old.
2. By the way, regardless of OSes and browsers, is it possible that a browser returns en instead of en-US?
I don't have a mac so I don't know, honestly speaking.