diff --git a/config/app.php b/config/app.php
index 13d4d22b..ea394b8e 100644
--- a/config/app.php
+++ b/config/app.php
@@ -14,6 +14,7 @@ return [
         \Engelsystem\Database\DatabaseServiceProvider::class,
         \Engelsystem\Http\RequestServiceProvider::class,
         \Engelsystem\Http\SessionServiceProvider::class,
+        \Engelsystem\Helpers\TranslationServiceProvider::class,
         \Engelsystem\Http\ResponseServiceProvider::class,
         \Engelsystem\Http\Psr7ServiceProvider::class,
         \Engelsystem\Middleware\RouteDispatcherServiceProvider::class,
@@ -24,6 +25,7 @@ return [
     'middleware' => [
         \Engelsystem\Middleware\SendResponseHandler::class,
         \Engelsystem\Middleware\ExceptionHandler::class,
+        \Engelsystem\Middleware\SetLocale::class,
         \Engelsystem\Middleware\RouteDispatcher::class,
         \Engelsystem\Middleware\RequestHandler::class,
     ],
diff --git a/includes/engelsystem.php b/includes/engelsystem.php
index eb5b220a..4c096b43 100644
--- a/includes/engelsystem.php
+++ b/includes/engelsystem.php
@@ -21,12 +21,6 @@ if ($app->get('config')->get('maintenance')) {
 }
 
 
-/**
- * Init translations
- */
-gettext_init();
-
-
 /**
  * Init authorization
  */
diff --git a/includes/helper/email_helper.php b/includes/helper/email_helper.php
index c223d026..8d1cb794 100644
--- a/includes/helper/email_helper.php
+++ b/includes/helper/email_helper.php
@@ -15,14 +15,16 @@ function engelsystem_email_to_user($recipient_user, $title, $message, $not_if_it
         return true;
     }
 
-    gettext_locale($recipient_user['Sprache']);
+    /** @var \Engelsystem\Helpers\Translator $translator */
+    $translator = app()->get('translator');
+    $locale = $translator->getLocale();
 
+    $translator->setLocale($recipient_user['Sprache']);
     $message = sprintf(_('Hi %s,'), $recipient_user['Nick']) . "\n\n"
         . _('here is a message for you from the engelsystem:') . "\n\n"
         . $message . "\n\n"
         . _('This email is autogenerated and has not been signed. You got this email because you are registered in the engelsystem.');
-
-    gettext_locale();
+    $translator->setLocale($locale);
 
     return engelsystem_email($recipient_user['email'], $title, $message);
 }
diff --git a/includes/helper/internationalization_helper.php b/includes/helper/internationalization_helper.php
deleted file mode 100644
index bb6d0abd..00000000
--- a/includes/helper/internationalization_helper.php
+++ /dev/null
@@ -1,80 +0,0 @@
-<?php
-
-/**
- * Return currently active locale
- *
- * @return string
- */
-function locale()
-{
-    return session()->get('locale');
-}
-
-/**
- * Returns two letter language code from currently active locale
- *
- * @return string
- */
-function locale_short()
-{
-    return substr(locale(), 0, 2);
-}
-
-/**
- * Initializes gettext for internationalization and updates the sessions locale to use for translation.
- */
-function gettext_init()
-{
-    $locales = config('locales');
-    $request = request();
-    $session = session();
-
-    if ($request->has('set_locale') && isset($locales[$request->input('set_locale')])) {
-        $session->set('locale', $request->input('set_locale'));
-    } elseif (!$session->has('locale')) {
-        $session->set('locale', config('default_locale'));
-    }
-
-    gettext_locale();
-    bindtextdomain('default', app('path.lang'));
-    bind_textdomain_codeset('default', 'UTF-8');
-    textdomain('default');
-}
-
-/**
- * Swich gettext locale.
- *
- * @param string $locale
- */
-function gettext_locale($locale = null)
-{
-    if (empty($locale)) {
-        $locale = session()->get('locale');
-    }
-
-    putenv('LC_ALL=' . $locale);
-    setlocale(LC_ALL, $locale);
-}
-
-/**
- * Renders language selection.
- *
- * @return array
- */
-function make_langselect()
-{
-    $request = app('request');
-
-    $items = [];
-    foreach (config('locales') as $locale => $name) {
-        $url = url($request->getPathInfo(), ['set_locale' => $locale]);
-
-        $items[] = toolbar_item_link(
-            htmlspecialchars($url),
-            '',
-            $name,
-            $locale == locale()
-        );
-    }
-    return $items;
-}
diff --git a/includes/includes.php b/includes/includes.php
index e316e550..7a68c3c9 100644
--- a/includes/includes.php
+++ b/includes/includes.php
@@ -61,7 +61,6 @@ $includeFiles = [
     __DIR__ . '/../includes/controller/user_worklog_controller.php',
 
     __DIR__ . '/../includes/helper/graph_helper.php',
-    __DIR__ . '/../includes/helper/internationalization_helper.php',
     __DIR__ . '/../includes/helper/message_helper.php',
     __DIR__ . '/../includes/helper/error_helper.php',
     __DIR__ . '/../includes/helper/email_helper.php',
diff --git a/includes/sys_form.php b/includes/sys_form.php
index 05df4c15..9cb6f38d 100644
--- a/includes/sys_form.php
+++ b/includes/sys_form.php
@@ -66,6 +66,9 @@ function form_date($name, $label, $value, $start_date = '', $end_date = '')
     $value = is_numeric($value) ? date('Y-m-d', $value) : '';
     $start_date = is_numeric($start_date) ? date('Y-m-d', $start_date) : '';
     $end_date = is_numeric($end_date) ? date('Y-m-d', $end_date) : '';
+    $locale = $locale = session()->get('locale');
+    $shortLocale = substr($locale, 0, 2);
+
     return form_element($label, '
     <div class="input-group date" id="' . $dom_id . '">
       <input name="' . $name . '" class="form-control" value="' . htmlspecialchars($value) . '">'
@@ -74,7 +77,7 @@ function form_date($name, $label, $value, $start_date = '', $end_date = '')
     <script type="text/javascript">
 			$(function(){
         $("#' . $dom_id . '").datepicker({
-				  language: "' . locale_short() . '",
+				  language: "' . $shortLocale . '",
           todayBtn: "linked",
           format: "yyyy-mm-dd",
           startDate: "' . $start_date . '",
diff --git a/includes/sys_menu.php b/includes/sys_menu.php
index 85ef1287..58d4bab3 100644
--- a/includes/sys_menu.php
+++ b/includes/sys_menu.php
@@ -110,7 +110,7 @@ function make_user_submenu()
 {
     global $privileges, $page;
 
-    $user_submenu = make_langselect();
+    $user_submenu = make_language_select();
 
     if (in_array('user_settings', $privileges) || in_array('logout', $privileges)) {
         $user_submenu[] = toolbar_item_divider();
@@ -227,6 +227,30 @@ function make_room_navigation($menu)
     return $menu;
 }
 
+/**
+ * Renders language selection.
+ *
+ * @return array
+ */
+function make_language_select()
+{
+    $request = app('request');
+    $activeLocale = session()->get('locale');
+
+    $items = [];
+    foreach (config('locales') as $locale => $name) {
+        $url = url($request->getPathInfo(), ['set-locale' => $locale]);
+
+        $items[] = toolbar_item_link(
+            htmlspecialchars($url),
+            '',
+            $name,
+            $locale == $activeLocale
+        );
+    }
+    return $items;
+}
+
 /**
  * @return string
  */
diff --git a/src/Helpers/TranslationServiceProvider.php b/src/Helpers/TranslationServiceProvider.php
new file mode 100644
index 00000000..9d86df7d
--- /dev/null
+++ b/src/Helpers/TranslationServiceProvider.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Engelsystem\Helpers;
+
+use Engelsystem\Config\Config;
+use Engelsystem\Container\ServiceProvider;
+use Symfony\Component\HttpFoundation\Session\Session;
+
+class TranslationServiceProvider extends ServiceProvider
+{
+    public function register()
+    {
+        /** @var Config $config */
+        $config = $this->app->get('config');
+        /** @var Session $session */
+        $session = $this->app->get('session');
+
+        $locales = $config->get('locales');
+        $locale = $config->get('default_locale');
+
+        $sessionLocale = $session->get('locale', $locale);
+        if (isset($locales[$sessionLocale])) {
+            $locale = $sessionLocale;
+        }
+
+        $this->initGettext();
+        $session->set('locale', $locale);
+
+        $translator = $this->app->make(
+            Translator::class,
+            ['locale' => $locale, 'locales' => $locales, 'localeChangeCallback' => [$this, 'setLocale']]
+        );
+        $this->app->instance(Translator::class, $translator);
+        $this->app->instance('translator', $translator);
+    }
+
+    /**
+     * @param string $textDomain
+     * @param string $encoding
+     * @codeCoverageIgnore
+     */
+    protected function initGettext($textDomain = 'default', $encoding = 'UTF-8')
+    {
+        bindtextdomain($textDomain, $this->app->get('path.lang'));
+        bind_textdomain_codeset($textDomain, $encoding);
+        textdomain($textDomain);
+    }
+
+    /**
+     * @param string $locale
+     * @codeCoverageIgnore
+     */
+    public function setLocale($locale)
+    {
+        putenv('LC_ALL=' . $locale);
+        setlocale(LC_ALL, $locale);
+    }
+}
diff --git a/src/Helpers/Translator.php b/src/Helpers/Translator.php
new file mode 100644
index 00000000..1e953a21
--- /dev/null
+++ b/src/Helpers/Translator.php
@@ -0,0 +1,105 @@
+<?php
+
+namespace Engelsystem\Helpers;
+
+class Translator
+{
+    /** @var string[] */
+    protected $locales;
+
+    /** @var string */
+    protected $locale;
+
+    /** @var callable */
+    protected $localeChangeCallback;
+
+    /**
+     * Translator constructor.
+     *
+     * @param string   $locale
+     * @param string[] $locales
+     * @param callable $localeChangeCallback
+     */
+    public function __construct(string $locale, array $locales = [], callable $localeChangeCallback = null)
+    {
+        $this->localeChangeCallback = $localeChangeCallback;
+
+        $this->setLocale($locale);
+        $this->setLocales($locales);
+    }
+
+    /**
+     * Get the translation for a given key
+     *
+     * @param string $key
+     * @param array  $replace
+     * @return string
+     */
+    public function translate(string $key, array $replace = []): string
+    {
+        $translated = $this->translateGettext($key);
+
+        if (!empty($replace)) {
+            $translated = call_user_func_array('sprintf', array_merge([$translated], $replace));
+        }
+
+        return $translated;
+    }
+
+    /**
+     * Translate the key via gettext
+     *
+     * @param string $key
+     * @return string
+     * @codeCoverageIgnore
+     */
+    protected function translateGettext(string $key): string
+    {
+        return _($key);
+    }
+
+    /**
+     * @return string
+     */
+    public function getLocale(): string
+    {
+        return $this->locale;
+    }
+
+    /**
+     * @param string $locale
+     */
+    public function setLocale(string $locale)
+    {
+        $this->locale = $locale;
+
+        if (is_callable($this->localeChangeCallback)) {
+            call_user_func_array($this->localeChangeCallback, [$locale]);
+        }
+    }
+
+    /**
+     * @return string[]
+     */
+    public function getLocales(): array
+    {
+        return $this->locales;
+    }
+
+    /**
+     * @param string $locale
+     * @return bool
+     */
+    public function hasLocale(string $locale): bool
+    {
+        return isset($this->locales[$locale]);
+    }
+
+    /**
+     * @param string[] $locales
+     */
+    public function setLocales(array $locales)
+    {
+        $this->locales = $locales;
+    }
+}
diff --git a/src/Middleware/SetLocale.php b/src/Middleware/SetLocale.php
new file mode 100644
index 00000000..86fa0b7f
--- /dev/null
+++ b/src/Middleware/SetLocale.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Engelsystem\Middleware;
+
+use Engelsystem\Helpers\Translator;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use Symfony\Component\HttpFoundation\Session\Session;
+
+class SetLocale implements MiddlewareInterface
+{
+    /** @var Translator */
+    protected $translator;
+
+    /** @var Session */
+    protected $session;
+
+    /**
+     * @param Translator $translator
+     * @param Session    $session
+     */
+    public function __construct(Translator $translator, Session $session)
+    {
+        $this->translator = $translator;
+        $this->session = $session;
+    }
+
+    /**
+     * Process an incoming server request and setting the locale if required
+     *
+     * @param ServerRequestInterface  $request
+     * @param RequestHandlerInterface $handler
+     * @return ResponseInterface
+     */
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $query = $request->getQueryParams();
+        if (isset($query['set-locale']) && $this->translator->hasLocale($query['set-locale'])) {
+            $locale = $query['set-locale'];
+
+            $this->translator->setLocale($locale);
+            $this->session->set('locale', $locale);
+        }
+
+        return $handler->handle($request);
+    }
+}
diff --git a/src/helpers.php b/src/helpers.php
index 336f81fe..3a182bf7 100644
--- a/src/helpers.php
+++ b/src/helpers.php
@@ -3,6 +3,7 @@
 
 use Engelsystem\Application;
 use Engelsystem\Config\Config;
+use Engelsystem\Helpers\Translator;
 use Engelsystem\Http\Request;
 use Engelsystem\Http\Response;
 use Engelsystem\Http\UrlGenerator;
@@ -118,6 +119,40 @@ function session($key = null, $default = null)
     return $session->get($key, $default);
 }
 
+/**
+ * Translate the given message
+ *
+ * @param  string $key
+ * @param  array  $replace
+ * @return string|Translator
+ */
+function trans($key = null, $replace = [])
+{
+    /** @var Translator $translator */
+    $translator = app('translator');
+
+    if (is_null($key)) {
+        return $translator;
+    }
+
+    return $translator->translate($key, $replace);
+}
+
+/**
+ * Translate the given message
+ *
+ * @param  string $key
+ * @param  array  $replace
+ * @return string
+ */
+function __($key, $replace = [])
+{
+    /** @var Translator $translator */
+    $translator = app('translator');
+
+    return $translator->translate($key, $replace);
+}
+
 /**
  * @param string $path
  * @param array  $parameters
diff --git a/tests/Unit/Helpers/TranslationServiceProviderTest.php b/tests/Unit/Helpers/TranslationServiceProviderTest.php
new file mode 100644
index 00000000..c5ba7386
--- /dev/null
+++ b/tests/Unit/Helpers/TranslationServiceProviderTest.php
@@ -0,0 +1,86 @@
+<?php
+
+namespace Engelsystem\Test\Unit\Helpers;
+
+use Engelsystem\Config\Config;
+use Engelsystem\Helpers\TranslationServiceProvider;
+use Engelsystem\Helpers\Translator;
+use Engelsystem\Test\Unit\ServiceProviderTest;
+use PHPUnit\Framework\MockObject\MockObject;
+use Symfony\Component\HttpFoundation\Session\Session;
+
+class TranslationServiceProviderTest extends ServiceProviderTest
+{
+    /**
+     * @covers \Engelsystem\Helpers\TranslationServiceProvider::register()
+     */
+    public function testRegister()
+    {
+        $app = $this->getApp(['make', 'instance', 'get']);
+        /** @var Config|MockObject $config */
+        $config = $this->createMock(Config::class);
+        /** @var Session|MockObject $session */
+        $session = $this->createMock(Session::class);
+        /** @var Translator|MockObject $translator */
+        $translator = $this->createMock(Translator::class);
+
+        /** @var TranslationServiceProvider|MockObject $serviceProvider */
+        $serviceProvider = $this->getMockBuilder(TranslationServiceProvider::class)
+            ->setConstructorArgs([$app])
+            ->setMethods(['initGettext', 'setLocale'])
+            ->getMock();
+
+        $serviceProvider->expects($this->once())
+            ->method('initGettext');
+
+        $app->expects($this->exactly(2))
+            ->method('get')
+            ->withConsecutive(['config'], ['session'])
+            ->willReturnOnConsecutiveCalls($config, $session);
+
+        $defaultLocale = 'fo_OO';
+        $locale = 'te_ST.WTF-9';
+        $locales = ['fo_OO' => 'Foo', 'fo_OO.BAR' => 'Foo (Bar)', 'te_ST.WTF-9' => 'WTF\'s Testing?'];
+        $config->expects($this->exactly(2))
+            ->method('get')
+            ->withConsecutive(
+                ['locales'],
+                ['default_locale']
+            )
+            ->willReturnOnConsecutiveCalls(
+                $locales,
+                $defaultLocale
+            );
+
+        $session->expects($this->once())
+            ->method('get')
+            ->with('locale', $defaultLocale)
+            ->willReturn($locale);
+        $session->expects($this->once())
+            ->method('set')
+            ->with('locale', $locale);
+
+        $app->expects($this->once())
+            ->method('make')
+            ->with(
+                Translator::class,
+                [
+                    'locale'               => $locale,
+                    'locales'              => $locales,
+                    'localeChangeCallback' => [$serviceProvider, 'setLocale']
+                ]
+            )
+            ->willReturn($translator);
+
+        $app->expects($this->exactly(2))
+            ->method('instance')
+            ->withConsecutive(
+                [Translator::class, $translator],
+                ['translator', $translator]
+            );
+
+        $serviceProvider->register();
+    }
+}
+
+
diff --git a/tests/Unit/Helpers/TranslatorTest.php b/tests/Unit/Helpers/TranslatorTest.php
new file mode 100644
index 00000000..396d2b65
--- /dev/null
+++ b/tests/Unit/Helpers/TranslatorTest.php
@@ -0,0 +1,69 @@
+<?php
+
+namespace Engelsystem\Test\Unit\Helpers;
+
+use Engelsystem\Helpers\Translator;
+use Engelsystem\Test\Unit\ServiceProviderTest;
+use PHPUnit\Framework\MockObject\MockObject;
+use stdClass;
+
+class TranslatorTest extends ServiceProviderTest
+{
+    /**
+     * @covers \Engelsystem\Helpers\Translator::__construct()
+     * @covers \Engelsystem\Helpers\Translator::setLocale()
+     * @covers \Engelsystem\Helpers\Translator::setLocales()
+     * @covers \Engelsystem\Helpers\Translator::getLocale()
+     * @covers \Engelsystem\Helpers\Translator::getLocales()
+     * @covers \Engelsystem\Helpers\Translator::hasLocale()
+     */
+    public function testInit()
+    {
+        $locales = ['te_ST.ER-01' => 'Tests', 'fo_OO' => 'SomeFOO'];
+        $locale = 'te_ST.ER-01';
+
+        /** @var callable|MockObject $callable */
+        $callable = $this->getMockBuilder(stdClass::class)
+            ->setMethods(['__invoke'])
+            ->getMock();
+        $callable->expects($this->exactly(2))
+            ->method('__invoke')
+            ->withConsecutive(['te_ST.ER-01'], ['fo_OO']);
+
+        $translator = new Translator($locale, $locales, $callable);
+
+        $this->assertEquals($locales, $translator->getLocales());
+        $this->assertEquals($locale, $translator->getLocale());
+
+        $translator->setLocale('fo_OO');
+        $this->assertEquals('fo_OO', $translator->getLocale());
+
+        $newLocales = ['lo_RM' => 'Lorem', 'ip_SU-M' => 'Ipsum'];
+        $translator->setLocales($newLocales);
+        $this->assertEquals($newLocales, $translator->getLocales());
+
+        $this->assertTrue($translator->hasLocale('ip_SU-M'));
+        $this->assertFalse($translator->hasLocale('te_ST.ER-01'));
+    }
+
+    /**
+     * @covers \Engelsystem\Helpers\Translator::translate()
+     */
+    public function testTranslate()
+    {
+        /** @var Translator|MockObject $translator */
+        $translator = $this->getMockBuilder(Translator::class)
+            ->setConstructorArgs(['de_DE.UTF-8', ['de_DE.UTF-8' => 'Deutsch']])
+            ->setMethods(['translateGettext'])
+            ->getMock();
+        $translator->expects($this->once())
+            ->method('translateGettext')
+            ->with('My favourite number is %u!')
+            ->willReturn('Meine Lieblingszahl ist die %u!');
+
+        $return = $translator->translate('My favourite number is %u!', [3]);
+        $this->assertEquals('Meine Lieblingszahl ist die 3!', $return);
+    }
+}
+
+
diff --git a/tests/Unit/HelpersTest.php b/tests/Unit/HelpersTest.php
index b59b11ee..20d3c2de 100644
--- a/tests/Unit/HelpersTest.php
+++ b/tests/Unit/HelpersTest.php
@@ -5,10 +5,11 @@ namespace Engelsystem\Test\Unit;
 use Engelsystem\Application;
 use Engelsystem\Config\Config;
 use Engelsystem\Container\Container;
+use Engelsystem\Helpers\Translator;
 use Engelsystem\Http\Request;
 use Engelsystem\Http\Response;
-use Engelsystem\Renderer\Renderer;
 use Engelsystem\Http\UrlGenerator;
+use Engelsystem\Renderer\Renderer;
 use PHPUnit\Framework\TestCase;
 use PHPUnit_Framework_MockObject_MockObject as MockObject;
 use Symfony\Component\HttpFoundation\Session\Session;
@@ -194,6 +195,29 @@ class HelpersTest extends TestCase
         $this->assertEquals('rendered template', view('template.name', ['template' => 'data']));
     }
 
+    /**
+     * @covers \__
+     * @covers \trans
+     */
+    public function testTrans()
+    {
+        /** @var Translator|MockObject $translator */
+        $translator = $this->getMockBuilder(Translator::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->getAppMock('translator', $translator);
+
+        $translator->expects($this->exactly(2))
+            ->method('translate')
+            ->with('Lorem %s Ipsum', ['foo'])
+            ->willReturn('Lorem foo Ipsum');
+
+        $this->assertEquals($translator, trans());
+        $this->assertEquals('Lorem foo Ipsum', trans('Lorem %s Ipsum', ['foo']));
+        $this->assertEquals('Lorem foo Ipsum', __('Lorem %s Ipsum', ['foo']));
+    }
+
     /**
      * @covers \url
      */
diff --git a/tests/Unit/Middleware/SetLocaleTest.php b/tests/Unit/Middleware/SetLocaleTest.php
new file mode 100644
index 00000000..c4e9d2a4
--- /dev/null
+++ b/tests/Unit/Middleware/SetLocaleTest.php
@@ -0,0 +1,71 @@
+<?php
+
+namespace Engelsystem\Test\Unit\Middleware;
+
+use Engelsystem\Helpers\Translator;
+use Engelsystem\Middleware\SetLocale;
+use PHPUnit\Framework\TestCase;
+use PHPUnit_Framework_MockObject_MockObject as MockObject;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use Symfony\Component\HttpFoundation\Session\Session;
+
+class SetLocaleTest extends TestCase
+{
+    /**
+     * @covers \Engelsystem\Middleware\SetLocale::__construct
+     * @covers \Engelsystem\Middleware\SetLocale::process
+     */
+    public function testRegister()
+    {
+        /** @var Translator|MockObject $translator */
+        $translator = $this->createMock(Translator::class);
+        /** @var Session|MockObject $session */
+        $session = $this->createMock(Session::class);
+        /** @var ServerRequestInterface|MockObject $request */
+        $request = $this->getMockForAbstractClass(ServerRequestInterface::class);
+        /** @var RequestHandlerInterface|MockObject $handler */
+        $handler = $this->getMockForAbstractClass(RequestHandlerInterface::class);
+        /** @var ResponseInterface|MockObject $response */
+        $response = $this->getMockForAbstractClass(ResponseInterface::class);
+
+        $locale = 'te_ST.UTF8';
+
+        $request->expects($this->exactly(3))
+            ->method('getQueryParams')
+            ->willReturnOnConsecutiveCalls(
+                [],
+                ['set-locale' => 'en_US.UTF8'],
+                ['set-locale' => $locale]
+            );
+
+        $translator->expects($this->exactly(2))
+            ->method('hasLocale')
+            ->withConsecutive(
+                ['en_US.UTF8'],
+                [$locale]
+            )
+            ->willReturnOnConsecutiveCalls(
+                false,
+                true
+            );
+        $translator->expects($this->once())
+            ->method('setLocale')
+            ->with($locale);
+
+        $session->expects($this->once())
+            ->method('set')
+            ->with('locale', $locale);
+
+        $handler->expects($this->exactly(3))
+            ->method('handle')
+            ->with($request)
+            ->willReturn($response);
+
+        $middleware = new SetLocale($translator, $session);
+        $middleware->process($request, $handler);
+        $middleware->process($request, $handler);
+        $middleware->process($request, $handler);
+    }
+}