How to detect the user's locale from the browser?

Installation

To implement locale detection in your PHP project, you can use the HTTP2 library. You can install it via Composer:

composer require pear/http2

Usage

After installing the HTTP2 library, you can utilize it in your PHP code to detect the user's locale. Here's a basic example:

<?php

namespace App\Http\Middleware;

use Closure;
use fbt\FbtConfig;
use fbt\Runtime\Shared\FbtHooks;
use Illuminate\Http\Request;

class RegisterFbt
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle(Request $request, Closure $next)
    {
        // Notice: locale of logged-in user is always preferred
        if (! $request->user()) {
            // List of supported languages
            $supportedLanguages = [
                'en'    => 'en_US',
                'en-UK' => 'en_UK',
                'de'    => 'de_DE',
                'de-AT' => 'de_AT',
                'cs'    => 'cs_CZ',
                'sk'    => 'sk_SK',
            ];

            $http = new \HTTP2();

            // Detect the user's language
            $clientLanguage = $http->negotiateLanguage($supportedLanguages, $fallbackLanguage = 'en');
            
            // Get the locale for the detected language
            $locale = $supportedLanguages[$clientLanguage];
            
            // Set the detected locale
            FbtConfig::set('locale', $locale);
        }

        return $next($request);
    }
}

then register the middleware in app/Http/Kernel.php:

protected $middlewareGroups = [
    'web' => [
        // ...
        \App\Http\Middleware\RegisterFbt::class,
    ],
    // ...
];

Explanation

HTTP Accept-Language Header

The negotiateLanguage() method works by parsing the HTTP Accept-Language header sent by the user's browser. This header contains information about the user's preferred languages in order of priority. The method then matches these languages against the provided list and returns the best match.

Fallback Locale

In case the user's preferred language is not available or cannot be determined, it's essential to have a fallback locale. This ensures that your application always defaults to a suitable language/locale even when the detection process fails.