Hi Yuko.
If you want to translate site like this https://translate.google.com/translate?hl=&sl=auto&tl=ja&u=https%3A%2F%2Fs-plugins.com%2F – it won’t be possible for payment popup to work properly. Since Google Translate is displaying a website inside of a iframe on their website, it breaks several security rules. So, unfortunately, it is not possible to make it work like this.
As I understand, you want your website to be available in two languages – Japanese and English, correct?