LocalizationMiddleware.php

<?php

namespace App\I18n;

use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;
use Zend\Diactoros\Response\RedirectResponse;
use Zend\I18n\Translator\Translator;
use Zend\Stratigility\MiddlewareInterface;

class LocalizationMiddleware implements MiddlewareInterface
{
    const LOCALE_ATTRIBUTE = 'locale';

    private $translator;

    private $languages;

    public function __construct(Translator $translator, array $languages)
    {
        $this->translator = $translator;
        $this->languages  = $languages;
    }

    public function __invoke(Request $request, Response $response, callable $next = null)
    {
        $locale = $requestLocale = $request->getAttribute('locale');

        // If there is no or an invalid locale
        if (! $locale || ! in_array(substr(trim($locale), 0, 2), $this->languages, true)) {
            // Fallback to first language
            $locale = $this->languages[0];

            // Try the user preferred locales
            foreach ($this->getLocales($request) as $userLocale => $factor) {
                if (in_array(substr(trim($userLocale), 0, 2), $this->languages, true)) {
                    $locale = $userLocale;
                    break;
                }
            }
        }

        // Only the language is needed
        $locale = substr(trim($locale), 0, 2);

        if ($request->getUri()->getPath() === '/') {
            // Redirect and set the locale for the homepage
            return new RedirectResponse('/' . $locale);
        }

        // Set current locale
        $this->translator->setLocale($locale);

        // Get response first, apply content language later
        if (null !== $next) {
            $response = $next($request->withAttribute(self::LOCALE_ATTRIBUTE, $locale), $response);
        }

        // Add the content language to the response
        return $response->withHeader('Content-Language', $locale);
    }

    private function getLocales(Request $request)
    {
        $locales = [];

        if (! array_key_exists('HTTP_ACCEPT_LANGUAGE', $request->getServerParams())) {
            return $locales;
        }

        // break up string into pieces (locales and q factors)
        preg_match_all('/([a-z]{1,8}(-[a-z]{1,8})?)\s*(;\s*q\s*=\s*(1|0\.[\d]+))?/i',
            $request->getServerParams()['HTTP_ACCEPT_LANGUAGE'], $matches);

        if (count($matches[1])) {
            // create a list like "en" => 0.8
            $locales = array_combine($matches[1], $matches[4]);

            // set default to 1 for any without q factor
            foreach ($locales as $locale => $factor) {
                if ($factor === '') {
                    $locales[$locale] = 1;
                }
            }

            // sort list based on value
            arsort($locales, SORT_NUMERIC);
        }

        return $locales;
    }
}