i18n lang should ignore uppercase/lowercase

I use Mac with locale zh_CN

In application.conf
application.langs="en,zh-CN"

and I add messages.zh-CN right.

Message of Chinese show right for Chrome, but wrong for Safari and Mozilla(show english words).

and if I change all zh-CN to zh-cn, Mozilla and Safari becomes right and Chrome becomes wrong.

and I check with
curl --header "Accept-Language:zh-CN" http://localhost:9000/products
curl --header "Accept-Language:zh-cn" http://localhost:9000/products

Best Regards!