In need of a web developer to fix language detection on some landing pages

I am running some adult landing pages that used to adapt to the language of the user’s browser.

They were made by a developer who has left my team.
https://girls2date.club/mature/bin/mob/c

The language used to automatically change to all of these languages depending on the browser language :
* English – en
* Spanish – es
* Slovakian – sk
* Dutch – nl
* French – fr
* Italian – it
* Swedish – sv
* Romanian – ro
* Czech – cs
* Serbian – sr
* German – de

Now the first page is always in english, and only the secondary pages are translated.