diff --git a/src/App/Adapters/WebAppAdapter.php b/src/App/Adapters/WebAppAdapter.php
index dfdb396e0..d15f77ccc 100644
--- a/src/App/Adapters/WebAppAdapter.php
+++ b/src/App/Adapters/WebAppAdapter.php
@@ -97,8 +97,6 @@ public function start(): ?int
         try {
             $this->initializeRequestResponse($this->request, $this->response);
 
-            $this->loadLanguage();
-
             if ($this->request->isMethod('OPTIONS')) {
                 stop();
             }
@@ -110,6 +108,8 @@ public function start(): ?int
 
             $this->initializeRouter($this->request);
 
+            $this->loadLanguage();
+
             info(HookManager::getInstance()->getRegistered(), ['tab' => Debugger::HOOKS]);
 
             if (current_middlewares()) {
diff --git a/src/Http/Request/HttpRequest.php b/src/Http/Request/HttpRequest.php
index 64672caaa..6da60fdf2 100644
--- a/src/Http/Request/HttpRequest.php
+++ b/src/Http/Request/HttpRequest.php
@@ -142,8 +142,9 @@ public static function setRequestParams(array $params)
 
     /**
      * Sets the uploaded files array merging handled $_FILES and parsed files
-     * @param array $rawInputFiles
+     * @param array $files
      * @throws BaseException
+     * @throws ReflectionException
      */
     public static function setUploadedFiles(array $files)
     {
diff --git a/src/Http/Traits/Request/Internal.php b/src/Http/Traits/Request/Internal.php
index e5dffbd5c..c937ce3ce 100644
--- a/src/Http/Traits/Request/Internal.php
+++ b/src/Http/Traits/Request/Internal.php
@@ -86,7 +86,7 @@ public static function create(
 
         if ($headers) {
             foreach ($headers as $name => $value) {
-                $server->set('HTTP_' . strtoupper($name), $value);
+                $server->set('HTTP_' . strtoupper(str_replace('-', '_', $name)), $value);
             }
         }
 
diff --git a/src/Libraries/Lang/Factories/LangFactory.php b/src/Libraries/Lang/Factories/LangFactory.php
index 268dad892..bfe23baf5 100644
--- a/src/Libraries/Lang/Factories/LangFactory.php
+++ b/src/Libraries/Lang/Factories/LangFactory.php
@@ -53,17 +53,39 @@ public static function get(): Lang
         }
 
         $isEnabled = filter_var(config()->get('lang.enabled'), FILTER_VALIDATE_BOOLEAN);
+        $supported = (array)config()->get('lang.supported');
+        $default = config()->get('lang.default');
 
-        $langSegmentIndex = (int)config()->get('lang.url_segment');
+        $queryLang = Request::getQueryParam('lang');
 
-        if (!empty(route_prefix()) && $langSegmentIndex == 1) {
-            $langSegmentIndex++;
+        $lang = $queryLang && in_array($queryLang, $supported)
+            ? $queryLang
+            : null;
+
+        if (empty($lang)) {
+            $segmentIndex = (int)config()->get('lang.url_segment');
+
+            if (!empty(route_prefix()) && $segmentIndex == 1) {
+                $segmentIndex++;
+            }
+
+            $segmentLang = Request::getSegment($segmentIndex);
+
+            $lang = $segmentLang && in_array($segmentLang, $supported)
+                ? $segmentLang
+                : null;
         }
 
-        $lang = Request::getSegment($langSegmentIndex);
+        if (empty($lang)) {
+            $acceptedLang = server()->acceptedLang();
 
-        if (empty($lang) || !in_array($lang, (array)config()->get('lang.supported'))) {
-            $lang = config()->get('lang.default');
+            $lang = $acceptedLang && in_array($acceptedLang, $supported)
+                ? $acceptedLang
+                : null;
+        }
+
+        if (empty($lang)) {
+            $lang = $default;
         }
 
         if (!$lang) {
@@ -71,7 +93,6 @@ public static function get(): Lang
         }
 
         $translator = new Translator($lang);
-
         return self::$instance = new Lang($lang, $isEnabled, $translator);
     }
-}
+}
\ No newline at end of file
diff --git a/tests/Unit/AppTestCase.php b/tests/Unit/AppTestCase.php
index ebafc50d6..e9d28ecb1 100644
--- a/tests/Unit/AppTestCase.php
+++ b/tests/Unit/AppTestCase.php
@@ -5,7 +5,9 @@
 use Quantum\Libraries\Storage\Factories\FileSystemFactory;
 use Quantum\App\Factories\AppFactory;
 use Quantum\Environment\Environment;
+use Quantum\Router\RouteController;
 use PHPUnit\Framework\TestCase;
+use Quantum\Http\Request;
 use Quantum\Loader\Setup;
 use ReflectionClass;
 use Quantum\App\App;
@@ -65,4 +67,24 @@ protected function removeFile(string $filePath)
             $this->fs->remove($filePath);
         }
     }
+
+    protected function testRequest(
+        string $uri,
+        string $method = 'GET',
+        array $body = [],
+        array $headers = []
+    )
+    {
+        $request = new Request();
+
+        $request->create($method, $uri, $body, $headers);
+
+        RouteController::setCurrentRoute([
+            "route" => "test",
+            "method" => $method,
+            "controller" => 'TestController',
+            "action" => 'testAction',
+            "module" => 'Test',
+        ]);
+    }
 }
\ No newline at end of file
diff --git a/tests/Unit/Libraries/Lang/Factories/LangFactoryTest.php b/tests/Unit/Libraries/Lang/Factories/LangFactoryTest.php
index e89d58c7b..afb888e31 100644
--- a/tests/Unit/Libraries/Lang/Factories/LangFactoryTest.php
+++ b/tests/Unit/Libraries/Lang/Factories/LangFactoryTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Quantum\Tests\Unit\Libraries\Lang;
+namespace Quantum\Tests\Unit\Libraries\Lang\Factories;
 
 use Quantum\Libraries\Lang\Exceptions\LangException;
 use Quantum\Libraries\Lang\Factories\LangFactory;
@@ -15,16 +15,9 @@ public function setUp(): void
         parent::setUp();
 
         $this->setPrivateProperty(LangFactory::class, 'instance', null);
-
-        config()->set('lang', [
-            'enabled' => true,
-            'default' => 'en',
-            'supported' => ['en', 'es'],
-            'url_segment' => 1
-        ]);
     }
 
-    public function testLangFactoryGetLangInstance(): void
+    public function testLangFactoryGetLangInstance()
     {
         $lang = LangFactory::get();
 
@@ -35,7 +28,7 @@ public function testLangFactoryGetLangInstance(): void
         $this->assertTrue($lang->isEnabled());
     }
 
-    public function testLangFactoryGetReturnsSameInstance(): void
+    public function testLangFactoryGetReturnsSameInstance()
     {
         $first = LangFactory::get();
 
@@ -44,20 +37,88 @@ public function testLangFactoryGetReturnsSameInstance(): void
         $this->assertSame($first, $second);
     }
 
-    public function testLangFactoryGetFallsBackToDefaultIfSegmentInvalid(): void
+    public function testLangFactoryDetectedFromRouteParameter()
+    {
+        $this->testRequest('http://127.0.0.1/es/api/rest');
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('es', $lang->getLang());
+    }
+
+    public function testLangFactoryDetectedFromQueryParameter()
+    {
+        $this->testRequest('http://127.0.0.1/api/rest?lang=es');
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('es', $lang->getLang());
+    }
+
+    public function testLangFactoryDetectedFromAcceptedLangParameter()
+    {
+        $this->testRequest('http://127.0.0.1/api/rest', 'GET', [], ['Accept-Language' => 'es, en;q=0.8, fr;q=0.6']);
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('es', $lang->getLang());
+    }
+
+    public function testLangFactoryFallsBackToDefaultIfNoLangDetected()
+    {
+        $this->testRequest('http://127.0.0.1/api/rest');
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('en', $lang->getLang());
+    }
+
+    public function testLangFactoryFallsBackToDefaultIfProvidedLangIsNotSupported()
     {
-        config()->set('lang.url_segment', 0);
+        config()->set('lang', [
+            'enabled' => true,
+            'default' => 'en',
+            'supported' => ['en', 'es'],
+            'url_segment' => 1
+        ]);
+
+        $this->testRequest('http://127.0.0.1/fr/api/rest');
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('en', $lang->getLang());
+
+        $this->setPrivateProperty(LangFactory::class, 'instance', null);
+
+        $this->testRequest('http://127.0.0.1/api/rest?lang=fr');
+
+        $lang = LangFactory::get();
+
+        $this->assertEquals('en', $lang->getLang());
+
+        $this->setPrivateProperty(LangFactory::class, 'instance', null);
+
+        $this->testRequest('http://127.0.0.1/api/rest', 'GET', [], ['Accept-Language' => 'fr, en;q=0.8, fr;q=0.6']);
 
         $lang = LangFactory::get();
 
         $this->assertEquals('en', $lang->getLang());
     }
 
-    public function testGetThrowsIfNoDefaultConfigured(): void
+    public function testLangFactoryThrowsErrorIfNoDefaultLangFound()
     {
+        config()->set('lang', [
+            'enabled' => true,
+            'default' => null,
+            'supported' => ['en', 'es'],
+            'url_segment' => 1
+        ]);
+
+        $this->testRequest('http://127.0.0.1/fr/api/rest');
+
         $this->expectException(LangException::class);
 
-        config()->set('lang.default', null);
+        $this->expectExceptionMessage('Misconfigured lang default config');
 
         LangFactory::get();
     }
diff --git a/tests/Unit/Libraries/Lang/Helpers/LangHelperFunctionsTest.php b/tests/Unit/Libraries/Lang/Helpers/LangHelperFunctionsTest.php
index 17d9efc21..00709e21b 100644
--- a/tests/Unit/Libraries/Lang/Helpers/LangHelperFunctionsTest.php
+++ b/tests/Unit/Libraries/Lang/Helpers/LangHelperFunctionsTest.php
@@ -14,12 +14,14 @@ public function setUp(): void
     {
         parent::setUp();
 
+        $this->setPrivateProperty(LangFactory::class, 'instance', null);
+
         $this->lang = LangFactory::get();
 
         $this->lang->load();
     }
 
-    public function testCurrentLang()
+    public function testLangHelperCurrentLang()
     {
         $this->assertEquals('en', current_lang());
 
@@ -28,14 +30,14 @@ public function testCurrentLang()
         $this->assertEquals('am', current_lang());
     }
 
-    public function testHelperT()
+    public function testLangHelperT()
     {
         $this->assertEquals('Testing', t('custom.test'));
 
         $this->assertEquals('Information about the new feature', t('custom.info', ['new']));
     }
 
-    public function testHelperUnderscoreT()
+    public function testLangHelperUnderscoreT()
     {
         ob_start();
 
@@ -46,7 +48,7 @@ public function testHelperUnderscoreT()
         $this->assertEquals('Testing', $output);
     }
 
-    public function testHelperTFail()
+    public function testLangHelperTFail()
     {
         $this->assertEquals('custom.non_existing_key', t('custom.non_existing_key'));
     }
diff --git a/tests/_root/modules/Test/resources/lang/es/custom.php b/tests/_root/modules/Test/resources/lang/es/custom.php
new file mode 100644
index 000000000..80ef6b057
--- /dev/null
+++ b/tests/_root/modules/Test/resources/lang/es/custom.php
@@ -0,0 +1,7 @@
+<?php
+
+return [
+    'learn_more' => 'Aprender más',
+    'info' => 'Información sobre la función {%1}',
+    'test' => 'Prueba'
+];
\ No newline at end of file
diff --git a/tests/_root/shared/config/lang.php b/tests/_root/shared/config/lang.php
index abd9dc007..56835fb06 100644
--- a/tests/_root/shared/config/lang.php
+++ b/tests/_root/shared/config/lang.php
@@ -7,7 +7,7 @@
      * ---------------------------------------------------------
      */
     'enabled' => true,
-    'supported' => ['en', 'ru', 'am'],
+    'supported' => ['en', 'es'],
     'default' => 'en',
     'url_segment' => 1,
 ];
\ No newline at end of file
diff --git a/tests/_root/shared/resources/lang/es/custom.php b/tests/_root/shared/resources/lang/es/custom.php
new file mode 100644
index 000000000..80ef6b057
--- /dev/null
+++ b/tests/_root/shared/resources/lang/es/custom.php
@@ -0,0 +1,7 @@
+<?php
+
+return [
+    'learn_more' => 'Aprender más',
+    'info' => 'Información sobre la función {%1}',
+    'test' => 'Prueba'
+];
\ No newline at end of file