Multi-language using laravel and vue

I am developing a page which will have multi-language Spanish and English , for front-end I am using vue-i18n . In front-end I send the active language every time I need some data of back-end

The problem

When I choose the language, I send the selected language to back-end , then I save it in sesion , but when I need laravel to return a message in the selected language, it returns it in Spanish (default language) ). Try this in AppServiceProvider

app()->setLocale(session()->has('lang') ? session()->get('lang') : 'es');

when I review the session it shows null .

When I save the session I save it like this

session()->put('lang', $request->input('lang'));
// o
session(['lang' => $request->input('lang')]);
    return response()->json([
        'lang' => app()->getLocale()
]);

why is the session not being saved? try using cookie or file in the driver and the problem persists.