Troubles with mobile menu with different languages

Hi! I hope you can help me and I didn't miss a post with the same problem.

I have created a website with 3 languages - people can switch the language in the navigation bar and the About page in the chosen language is opened in a new tab. Works perfectly fine, but I noticed recently that we have issues on mobiles. The website opens the new tab in the correct language, footer is of course in the chosen language, but the hidden navigation bar stays in English. So as soon as I want to switch to a different page,  I get redirected to the chosen page in English. Apart from the About page (and the pages linked with the footer), nothing is accessible in Spanish or German as long as the navigation bar is not shown. Can anybody help? Very frustrating! 

https://phoenix.show/