example silex app for custom parsing of accept-header and matching it to a locale

silex-language-api-custom-locale-parsing.php

<?php

require_once __DIR__ . '/../vendor/autoload.php';

use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\AcceptHeader;

$app = new Silex\Application();

$app->before(function (Request $request) use ($app) {
    $languages = ['en', 'pt_BR', 'ja', 'zh', 'zh_Hans'];

    $locale = getPrefferedLanguage(
        $languages,
        $request->headers->get('Accept-Language')
    );

    $app['locale'] = $locale;
    $app['contentLanguage'] = str_replace('_', '-', $locale);
});

$app->after(function (Request $request, Response $response) use ($app) {
    $response->headers->set('Content-Language', $app['contentLanguage']);
});

$app->get('/', function () use ($app) {
    return new JsonResponse(
        [
            'locale' => $app['locale'],
            'contentLanguage' => $app['contentLanguage']
        ]
    );
});

$app->run();

function getPrefferedLanguage($locales, $acceptLanguageHeader)
{
    $acceptLanguages = array_keys(
        AcceptHeader::fromString(
            $acceptLanguageHeader
        )->all()
    );

    foreach ($acceptLanguages as $languageTag) {
        $subtags = explode('-', $languageTag);
        do {
            $tag = implode('_', $subtags);
            if (in_array($tag, $locales)) {
                return $tag;
            }
            array_pop($subtags);
        } while (count($subtags) > 0);
    }

    return $locales[0];

}