Wordpress plugin polylang always show en-US in other languages

I have got a problem with current languages. There is 3 languages (en/fr/vi) on my blog. On my blog, i installed wordpress 4.3, polylang 1.7.2 and already deactived other plugins. EN is default language. But when i get pll_current_language() in fr/vi is always return to "en". I event tested it with wordpress theme.

I found a article near the same my problem : http://ift.tt/1Q5xr0b the language_attributes() always return to "en-US".

Anybody got the same problem? Could you help me fix it?

Thanks

via Chebli Mohamed