Update PS cookie lang by external PHP

[sillusion]

Hi PS Community,

I'm working on a "quite complex" projet, and i'm struggling with multilingual navigation. My question is about updating Cookie Language.

Here is my Prestashop 1.6.1 featuring a Wordpress area : https://www.gaston-mercier.com/pages/ (WP home FR)
Multilingual nav (top right) is ok for posts, taxnomys, but i'm still in hard time for Homepage of Wordpress. Yes, i do know this is a Prestashop forum ! 
Here is my WP home EN : https://www.gaston-mercier.com/en/pages/ 

Here are some lines i already use : 

// catching WP lang : iso code
// translating to PS wording : INT $current_lang_id

// getting context
$context = Context::getContext();
// assign ID value to id_lang 
$context->smarty->assign(array('id_lang' => $current_lang_id));
// other way to assign value
$context->cookie->id_lang = $current_lang_id;

WP multilingual system created WP home EN at https://www.gaston-mercier.com/pages/?lang=en  so I created a redirection in PS from https://www.gaston-mercier.com/en/pages/ to https://www.gaston-mercier.com/pages/?lang=en . I thought going with /en/ may updates the PS language cookie. 
Sometimes it works (all content in EN), and sometimes it doesn't (content in FR). I don't understand how / why.

If i go to PS home, then turn to EN, i can navigate through entire website in EN, including WP, and getting back to FR from everywhere.

But switching language at this WP homepage is so cryptic !

Can anybody help ? Thanks ! :-) 
 

[Knowband Plugins]

I believe you using the correct code to change the Prestashop language 

This line is not required. 

$context->smarty->assign(array('id_lang' => $current_lang_id));

You just have to set the language id in the context. Also, check by adding lang object in context as mentioned in the below code.

$lang_id = 2;
$lang_obj = new Language($lang_id);
$this->context->language = $lang_obj;
$this->context->cookie->id_lang = $lang_id;