Basic use of TranslationServiceProvider in Silex - translation

Question

I'm trying to use the Silex TranslationServiceProvider in the most straighforward way i.e.
<?php
// web/index.php
require_once __DIR__.'/../vendor/autoload.php';
$app = new Silex\Application();
$app->register(new Silex\Provider\TranslationServiceProvider(), array(
'locale' => 'fr',
'locale_fallbacks' => array('en')
));
$app['translator.domains'] = array(
'messages' => array(
'en' => array('message_1' => 'Hello!'),
'fr' => array('message_1' => 'Bonjour')
));
echo $app['translator']->trans('message_1');
// I get 'Hello!' (why ?)
It seems that the 'locale' => 'fr' line when initializing the TranslationServiceProvider is not taken into account and that the only parameter that counts is locale_fallbacks (when I change locale_fallbacks to 'fr', the message is displayed in french)
Is there something very simple I am missing here ?
Thanks in advance
Edit
When I use the the setLocale function, it still doesn't work and seems to override the locale_fallbacks:
$app->register(new Silex\Provider\TranslationServiceProvider(), array(
'locale_fallbacks' => array('en')
));
$app['translator']->setLocale('fr');
echo $app['translator']->getLocale(); // returns 'fr' as expected
$app['translator.domains'] = array(
'messages' => array(
'en' => array('message_1' => 'Hello!'),
'fr' => array('message_1' => 'Bonjour')
));
echo $app['translator']->trans('message_1');
// now returns 'message_1' (??)
What's wrong with the way I use the provider ?

Answer 1

You must set the locale, otherwise the fallback is used:
$app['translator']->setLocale('fr');
I'm setting the locale in a $app->before() handler:
$app->before(function(Request $request) use ($app) {
// default language
$locale = 'en';
// quick and dirty ... try to detect the favorised language - to be improved!
if (!is_null($request->server->get('HTTP_ACCEPT_LANGUAGE'))) {
$langs = array();
// break up string into pieces (languages and q factors)
preg_match_all('/([a-z]{1,8}(-[a-z]{1,8})?)\s*(;\s*q\s*=\s*(1|0\.[0-9]+))?/i',
$request->server->get('HTTP_ACCEPT_LANGUAGE'), $lang_parse);
if (count($lang_parse[1]) > 0) {
foreach ($lang_parse[1] as $lang) {
if (false === (strpos($lang, '-'))) {
// only the country sign like 'de'
$locale = strtolower($lang);
} else {
// perhaps something like 'de-DE'
$locale = strtolower(substr($lang, 0, strpos($lang, '-')));
}
break;
}
}
$app['translator']->setLocale($locale);
$app['monolog']->addDebug('Set locale to '.$locale);
}
});

Answer 2

Two remarks on Ralf’s answer:
Almost all that is done in the before() middleware in unnecessary, as the Request class provides a convenience method for determining the “best” language based on the “Accept-Language” header. So basically, nothing more than this is required:
$app->before(
function (Request $request) use ($app) {
$app['translator']->setLocale($request->getPreferredLanguage(['en', 'fr']));
}
);
Silex uses the “magic” variable “{_locale}” in a route’s definition to set the locale accordingly. This means you do neither need to declare the locale when instantiating TranslationServiceProvider, nor call setLocale(), but simply declare the route like this:
$app->get('/{_locale}/path', ...);
Now, Twig and $app['translator'] (inside the Closure or controller method) will automatically be set to the correct locale.