Facebook Login redirect language problem

Hi on my website https://www.kawaii.com I have two languages. English and Japanese.

After Japanese user sign in with Facebook- they always get redirected to the English version of the page that should be Japanese, although I set to “reload current page” in Facebook Integration.

Example. Japansese user starts here: https://www.kawaii.com/ja/register

and uses facebook login. He should that land on    https://www.kawaii.com/ja/your-free-kawaii-email/

but instead he is landing here:  https://www.kawaii.com/your-free-kawaii-email/

Any Idea ?