Search bar display according to the language of the site

[ Moderator note: moved to Fixing WordPress. ]

Hello,

I manage a seasonal rental site and my channel manager has provided me with a documentation containing the steps to go through to display a search bar on my site, here is the link: https://alpine-residences.fr/

Currently the bar is displayed correctly only, it is displayed only in french whatever the language chosen on my site. I currently have an English and French version.

The channel manager gave me these codes:

INGLES
--------------

<?php

echo file_get_contents("https://booking.alpine-residences.fr/rentals/formularioMiniOptimized.php?bk=bk_alpineresidences&Idioma=EN&Fajax=1");
?>

FRANCES
--------------

<?php

echo file_get_contents("https://booking.alpine-residences.fr/location/formularioMiniOptimized.php?bk=bk_alpineresidences&Idioma=FR&Fajax=1");
?>

My problem is that I can not make sure that the bar (French version) is displayed for the French site and vice versa.

That’s what I did:

if($_GET['lang'] == "en") {
echo file_get_contents("https://booking.alpine-residences.fr/rentals/formularioMiniOptimized.php?bk=bk_alpineresidences&Idioma=EN&Fajax=1");

} else {

echo file_get_contents("https://booking.alpine-residences.fr/location/formularioMiniOptimized.php?bk=bk_alpineresidences&Idioma=FR&Fajax=1");
}
?>

Could you help me out and guide me on what does not work in my code?

Thank you in advance for your help!