歴史
[2] Web Applications 1.0 r8458 Add navigator.getLanguages() and <body onlanguagechange=''>
( ( 版))
http://html5.org/tools/web-apps-tracker?from=8457&to=8458
[1] Bug 21289 – Notification of change to navigator.language (locale change)
( ( 版))
https://www.w3.org/Bugs/Public/show_bug.cgi?id=21289