Fix #62 - Declare the language property

Author: williamdes

src/Doctum.php

@@ -195,6 +195,8 @@ class Doctum implements ArrayAccess
     private $base_url = null;
     /** @var string|null */
     private $favicon = null;
+    /** @var string */
+    private $language = 'en';
 
     /**
      * @var array<string,string>|null
@@ -362,7 +364,7 @@ public function offsetGet($offset)
     private function getLanguageFromConfig(): string
     {
         /** @var string $language */
-        $language = $this->config['language'] ?? 'en';
+        $language = $this->config['language'] ?? $this->language;
         return $language;
     }