diff --git a/I18n.php b/I18n.php
index f6d419f..29641dd 100644
--- a/I18n.php
+++ b/I18n.php
@@ -4,10 +4,8 @@
 
 use Koded\Stdlib\Config;
 use Throwable;
-use function error_log;
 use function ini_set;
 use function strtr;
-use function substr_count;
 use function vsprintf;
 
 interface I18nFormatter
@@ -65,16 +63,16 @@ public static function translate(
         string $locale = null): string
     {
         try {
-            return static::$catalogs[$locale]->translate('messages', $string, $arguments);
+            return self::$catalogs[$locale]->translate('messages', $string, $arguments);
         } catch (Throwable) {
-            static::registerCatalog($locale ??= static::locale());
-            return static::$catalogs[$locale]->translate('messages', $string, $arguments);
+            self::registerCatalog($locale ??= self::locale());
+            return self::$catalogs[$locale]->translate('messages', $string, $arguments);
         }
     }
 
     public static function locale(): string
     {
-        return static::$locale ??= static::normalizeLocale(\Locale::getDefault());
+        return self::$locale ??= I18nCatalog::normalizeLocale(\Locale::getDefault());
     }
 
     /**
@@ -82,7 +80,7 @@ public static function locale(): string
      */
     public static function catalogs(): array
     {
-        return static::$catalogs;
+        return self::$catalogs;
     }
 
     /**
@@ -91,7 +89,7 @@ public static function catalogs(): array
     public static function info(): array
     {
         $catalogs = [];
-        foreach (static::$catalogs as $locale => $instance) {
+        foreach (self::$catalogs as $locale => $instance) {
             $catalogs[$locale] = [
                 'class' => $instance::class,
                 'formatter' => $instance->formatter()::class,
@@ -100,7 +98,7 @@ public static function info(): array
             ];
         }
         return [
-            'locale' => static::$locale,
+            'locale' => self::$locale,
             'catalogs' => $catalogs,
         ];
     }
@@ -110,52 +108,43 @@ public static function register(
         bool        $asDefault = false): void
     {
         $locale = $catalog->locale();
-        if ($asDefault || empty(static::$catalogs)) {
-            static::setDefaultLocale($locale);
-            static::$directory = $catalog->directory();
-            static::$formatter = $catalog->formatter()::class;
-            static::$catalog = $catalog::class;
+        if ($asDefault || empty(self::$catalogs)) {
+            self::setDefaultLocale($locale);
+            self::$directory = $catalog->directory();
+            self::$formatter = $catalog->formatter()::class;
+            self::$catalog = $catalog::class;
         }
-        static::$catalogs[$locale] = $catalog;
+        self::$catalogs[$locale] = $catalog;
     }
 
     public static function flush(): void
     {
-        static::$catalogs = [];
-        static::$directory = null;
-        static::$formatter = null;
-        static::$catalog = null;
-        static::$locale = null;
+        self::$catalogs = [];
+        self::$directory = null;
+        self::$formatter = null;
+        self::$catalog = null;
+        self::$locale = null;
         ini_set('intl.default_locale', '');
         \Locale::setDefault('');
     }
 
     private static function registerCatalog(string $locale): void
     {
-        if (isset(static::$catalogs[$locale])) {
+        if (isset(self::$catalogs[$locale])) {
             return;
         }
-        static::$catalogs[$locale] = I18nCatalog::new((new Config)
+        self::$catalogs[$locale] = I18nCatalog::new((new Config)
             ->set('translation.locale', $locale)
-            ->set('translation.dir', static::$directory)
-            ->set('translation.formatter', static::$formatter)
-            ->set('translation.catalog', static::$catalog)
+            ->set('translation.dir', self::$directory)
+            ->set('translation.formatter', self::$formatter)
+            ->set('translation.catalog', self::$catalog)
         );
     }
 
     private static function setDefaultLocale(string $locale): void
     {
-        static::$locale = $locale;
+        self::$locale = $locale;
         ini_set('intl.default_locale', $locale);
         \Locale::setDefault($locale);
     }
-
-    private static function normalizeLocale(string $locale): string
-    {
-        if (substr_count($locale, '_') > 1) {
-            $locale = explode('_', $locale);
-            $locale = "$locale[0]_$locale[1]";
-        }
-        return $locale;
-    }
 }
diff --git a/I18nCatalog.php b/I18nCatalog.php
index 28267cc..3a6abaf 100644
--- a/I18nCatalog.php
+++ b/I18nCatalog.php
@@ -31,13 +31,13 @@ public static function new(Configuration $conf): I18nCatalog
         $instance = new $catalog(
             new $formatter,
             $directory = $conf->get('translation.dir', getcwd() . '/locales'),
-            $locale = $conf->get('translation.locale', I18n::DEFAULT_LOCALE)
+            $locale = self::normalizeLocale($conf->get('translation.locale', I18n::DEFAULT_LOCALE))
         );
         if ($instance->supports($locale)) {
             return $instance;
         }
         if ($catalog !== ArrayCatalog::class) {
-            error_log(" > ($locale) gettext not supported, try ArrayCatalog ...");
+            error_log(" > ($locale) gettext not supported, trying ArrayCatalog ...");
             $conf->set('translation.catalog', ArrayCatalog::class);
             return static::new($conf);
         }
@@ -45,6 +45,16 @@ public static function new(Configuration $conf): I18nCatalog
         return new NoCatalog(new $formatter, $directory, $locale);
     }
 
+    public static function normalizeLocale(string $locale): string
+    {
+        $locale = str_replace('.', '_', $locale);
+        if (substr_count($locale, '_') > 1) {
+            $locale = explode('_', $locale);
+            $locale = "$locale[0]_$locale[1]";
+        }
+        return $locale;
+    }
+
     public function translate(
         string $domain,
         string $key,
@@ -114,6 +124,7 @@ protected function supports(string $locale): bool
     {
         return true;
     }
+
     // @codeCoverageIgnoreEnd
 
     protected function initialize(string $locale): string|false
@@ -141,7 +152,7 @@ protected function initialize(string $locale): string|false
         try {
             $this->data = require($catalog = "$this->directory/$locale.php");
             if (false === array_key_exists('messages', $this->data)) {
-                error_log("i18n catalog $catalog is missing the messages array");
+                error_log("ERROR : i18n catalog $catalog is missing the messages array");
                 return false;
             }
             return $locale;
diff --git a/functions.php b/functions.php
index 604da19..32a4945 100644
--- a/functions.php
+++ b/functions.php
@@ -4,7 +4,7 @@
 
 function __(
     string $string,
-    array $arguments = [],
+    array  $arguments = [],
     string $locale = null): string
 {
     return I18n::translate($string, $arguments, $locale);
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 8b5c9ce..0337dcf 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -6,21 +6,21 @@
          verbose="true"
          colors="true"
 >
-  <coverage>
-    <include>
-      <directory suffix=".php">./</directory>
-    </include>
-    <exclude>
-      <directory>vendor</directory>
-      <directory>tests</directory>
-    </exclude>
-  </coverage>
-  <testsuites>
-    <testsuite name="Koded I18n Test Suite">
-      <directory>./tests</directory>
-    </testsuite>
-  </testsuites>
-  <php>
-    <ini name="date.timezone" value="UTC"/>
-  </php>
+    <coverage>
+        <include>
+            <directory suffix=".php">./</directory>
+        </include>
+        <exclude>
+            <directory>vendor</directory>
+            <directory>tests</directory>
+        </exclude>
+    </coverage>
+    <testsuites>
+        <testsuite name="Koded I18n Test Suite">
+            <directory>./tests</directory>
+        </testsuite>
+    </testsuites>
+    <php>
+        <ini name="date.timezone" value="UTC"/>
+    </php>
 </phpunit>
\ No newline at end of file
diff --git a/tests/Fixtures/xx_XX.php b/tests/Fixtures/xx_XX.php
new file mode 100644
index 0000000..25058db
--- /dev/null
+++ b/tests/Fixtures/xx_XX.php
@@ -0,0 +1,5 @@
+<?php
+
+return [
+
+];
\ No newline at end of file
diff --git a/tests/Unit/InvalidArrayCatalogTest.php b/tests/Unit/InvalidArrayCatalogTest.php
new file mode 100644
index 0000000..4f999f0
--- /dev/null
+++ b/tests/Unit/InvalidArrayCatalogTest.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Tests\Koded\I18n\Unit;
+
+use Koded\I18n\ArrayCatalog;
+use Koded\I18n\I18n;
+use Koded\I18n\I18nCatalog;
+use Koded\I18n\NoCatalog;
+use Koded\Stdlib\Config;
+
+class InvalidArrayCatalogTest extends I18nTestCase
+{
+    public function test_invalid_array()
+    {
+        I18n::register(I18nCatalog::new((new Config)
+            ->set('translation.locale', 'xx_XX')
+            ->set('translation.dir', __DIR__ . '/../Fixtures')
+            ->set('translation.catalog', ArrayCatalog::class)
+        ));
+
+        $this->assertInstanceOf(NoCatalog::class, I18n::catalogs()['xx_XX'],
+            'Expected ArrayCatalog, but it fallback to NoCatalog (invalid array)');
+    }
+}
diff --git a/tests/Unit/NormalizeLocaleTest.php b/tests/Unit/NormalizeLocaleTest.php
new file mode 100644
index 0000000..9de0749
--- /dev/null
+++ b/tests/Unit/NormalizeLocaleTest.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Tests\Koded\I18n\Unit;
+
+use Koded\I18n\I18n;
+use Koded\I18n\I18nCatalog;
+use Koded\I18n\NoCatalog;
+use Koded\Stdlib\Config;
+use PHPUnit\Framework\TestCase;
+
+class NormalizeLocaleTest extends TestCase
+{
+    public function test_should_normalize_locale()
+    {
+        $this->assertSame('mk_MK', I18n::catalogs()['mk_MK']->locale(),
+            'The locale is normalized');
+    }
+
+    protected function setUp(): void
+    {
+        I18n::register(I18nCatalog::new((new Config)
+            ->set('translation.catalog', NoCatalog::class)
+            ->set('translation.locale', 'mk_MK_UTF8')
+        ));
+    }
+
+    protected function tearDown(): void
+    {
+        I18n::flush();
+    }
+}