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.