Multi language website - on Firefox displaying both languages

Hi, I need 2 languages on my website and I started to implement the solution suggested in

It works in general, but I noticed that it does not work on firefox 67.0.4 on just one of my computers (mac 12 inches ) - show both the languages, instead of hiding one of te two.


Here is my site Read-Only:

https://preview.webflow.com/preview/sato-code-c7d394-fc8715e023e853dfae9014?utm_medium=preview_link&utm_source=designer&utm_content=sato-code-c7d394-fc8715e023e853dfae9014&preview=9793409639c692e0751eedfd9f0dd73e&mode=preview

Is there anything I can do?