diff --git a/Auth/Auth.php b/Auth/Auth.php
index 6f429b4fc..468fd9aa2 100644
--- a/Auth/Auth.php
+++ b/Auth/Auth.php
@@ -70,17 +70,17 @@ class Auth
     /**
      * Authenticates user.
      *
-     * @return mixed
+     * @return int
      *
      * @since  1.0.0
      * @author Dennis Eichhorn <d.eichhorn@oms.com>
      */
-    public function authenticate()
+    public function authenticate() : int
     {
         $uid = $this->session->get('UID');
 
-        if ($uid === null) {
-            $uid = false;
+        if (empty($uid)) {
+            return 0;
         }
 
         return $uid;
diff --git a/Localization/L11nManager.php b/Localization/L11nManager.php
index b4b6e43d8..6ed90d66f 100644
--- a/Localization/L11nManager.php
+++ b/Localization/L11nManager.php
@@ -59,7 +59,7 @@ class L11nManager
      * @since  1.0.0
      * @author Dennis Eichhorn <d.eichhorn@oms.com>
      */
-    public function __construct(LoggerInterface $logger)
+    public function __construct(LoggerInterface $logger = null)
     {
         $this->logger = $logger;
     }
@@ -179,9 +179,11 @@ class L11nManager
             $this->loadLanguage($code, $module, $class::getLocalization($code, $theme));
 
             if (!isset($this->language[$code][$module][$translation])) {
-                $this->logger->warning(FileLogger::MSG_FULL, [
-                    'message' => 'Undefined translation for \'' . $code . '/' . $module . '/' . $translation . '\'.',
-                ]);
+                if(isset($this->logger)) {
+                    $this->logger->warning(FileLogger::MSG_FULL, [
+                        'message' => 'Undefined translation for \'' . $code . '/' . $module . '/' . $translation . '\'.',
+                    ]);
+                }
 
                 return 'ERROR';
             }
diff --git a/Log/FileLogger.php b/Log/FileLogger.php
index 77b31acbb..50c3c9545 100644
--- a/Log/FileLogger.php
+++ b/Log/FileLogger.php
@@ -311,7 +311,7 @@ class FileLogger implements LoggerInterface
     private function write(string $message) /* : void */
     {
         $this->createFile();
-        if(!is_readable($this->path)) {
+        if(!is_writable($this->path)) {
             return;
         }
 
diff --git a/System/File/Local/File.php b/System/File/Local/File.php
index fed52659b..7271bd188 100644
--- a/System/File/Local/File.php
+++ b/System/File/Local/File.php
@@ -350,7 +350,7 @@ class File extends FileAbstract implements FileInterface
                 Directory::create(dirname($path), 0644, true);
             }
 
-            if(!is_writable($path)) {
+            if(!is_writable(dirname($path))) {
                 return false;
             }
             
diff --git a/Utils/Compression/LZW.php b/Utils/Compression/LZW.php
index 2f0e3bcda..0e296beb0 100644
--- a/Utils/Compression/LZW.php
+++ b/Utils/Compression/LZW.php
@@ -82,7 +82,7 @@ class LZW implements CompressionInterface
         }
 
         $w      = chr($compressed[0]);
-        $result = $w;
+        $result = $dictionary[$compressed[0]];
         $count  = count($compressed);
 
         for ($i = 1; $i < $count; $i++) {