diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 48a63a2..ca467af 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -7,6 +7,7 @@ Yii Framework 2 Change Log
 
 - Enh #11490: Added `yii\data\ArrayDataProvider::$modelClass` property to specify a model used to provide column labels even when data array is empty (PowerGamer1)
 - Bug #9950: Updated `yii\grid\DataColumn::getHeaderCellLabel()` to extract attribute label from the `filterModel` of Grid (silverfire)
+- Bug #11429: Fixed `yii\i18n\PhpMessageSource::loadFallbackMessages()` not to log error when source and language is same, but locales are different (silverfire)
 - Enh #11428: Speedup SQL query in `yii\db\oci\Schema::findColumns()` (SSiwek)
 - Enh #11414: Files specified as `null` in `yii\web\AssetBundle` won't be registered (Razzwan)
 - Enh #11432: Added HTTP status 421 "Misdirected Request" to list of statuses in `yii\web\Response` (dasmfm)
diff --git a/framework/i18n/GettextMessageSource.php b/framework/i18n/GettextMessageSource.php
index 215a977..18981a6 100644
--- a/framework/i18n/GettextMessageSource.php
+++ b/framework/i18n/GettextMessageSource.php
@@ -103,7 +103,11 @@ class GettextMessageSource extends MessageSource
         $fallbackMessageFile = $this->getMessageFilePath($fallbackLanguage);
         $fallbackMessages = $this->loadMessagesFromFile($fallbackMessageFile, $category);
 
-        if ($messages === null && $fallbackMessages === null && $fallbackLanguage !== $this->sourceLanguage) {
+        if (
+            $messages === null && $fallbackMessages === null
+            && $fallbackLanguage !== $this->sourceLanguage
+            && $fallbackLanguage !== substr($this->sourceLanguage, 0, 2)
+        ) {
             Yii::error("The message file for category '$category' does not exist: $originalMessageFile "
                 . "Fallback file does not exist as well: $fallbackMessageFile", __METHOD__);
         } elseif (empty($messages)) {
diff --git a/framework/i18n/PhpMessageSource.php b/framework/i18n/PhpMessageSource.php
index 388954a..1aa4a8a 100644
--- a/framework/i18n/PhpMessageSource.php
+++ b/framework/i18n/PhpMessageSource.php
@@ -105,7 +105,11 @@ class PhpMessageSource extends MessageSource
         $fallbackMessageFile = $this->getMessageFilePath($category, $fallbackLanguage);
         $fallbackMessages = $this->loadMessagesFromFile($fallbackMessageFile);
 
-        if ($messages === null && $fallbackMessages === null && $fallbackLanguage !== $this->sourceLanguage) {
+        if (
+            $messages === null && $fallbackMessages === null 
+            && $fallbackLanguage !== $this->sourceLanguage
+            && $fallbackLanguage !== substr($this->sourceLanguage, 0, 2)
+        ) {
             Yii::error("The message file for category '$category' does not exist: $originalMessageFile "
                 . "Fallback file does not exist as well: $fallbackMessageFile", __METHOD__);
         } elseif (empty($messages)) {
diff --git a/tests/framework/i18n/DbMessageSourceTest.php b/tests/framework/i18n/DbMessageSourceTest.php
index ba6ffa7..8215d73 100644
--- a/tests/framework/i18n/DbMessageSourceTest.php
+++ b/tests/framework/i18n/DbMessageSourceTest.php
@@ -29,13 +29,19 @@ class DbMessageSourceTest extends I18NTest
     {
         $this->i18n = new I18N([
             'translations' => [
-                'test' => new DbMessageSource([
+                'test' => [
+                    'class' => $this->getMessageSourceClass(),
                     'db' => static::$db,
-                ])
+                ]
             ]
         ]);
     }
 
+    private function getMessageSourceClass()
+    {
+        return DbMessageSource::className();
+    }
+
     protected static function runConsoleAction($route, $params = [])
     {
         if (Yii::$app === null) {
@@ -153,4 +159,10 @@ class DbMessageSourceTest extends I18NTest
         $this->assertEquals('Hallo Welt!', $this->i18n->translate('test', 'Hello world!', [], 'de-DE'));
         Event::off(DbMessageSource::className(), DbMessageSource::EVENT_MISSING_TRANSLATION);
     }
+
+
+    public function testIssue11429($sourceLanguage = null)
+    {
+        $this->markTestSkipped('DbMessageSource does not produce any errors when messages file is missing.');
+    }
 }
diff --git a/tests/framework/i18n/I18NTest.php b/tests/framework/i18n/I18NTest.php
index 4b09231..5b558e5 100644
--- a/tests/framework/i18n/I18NTest.php
+++ b/tests/framework/i18n/I18NTest.php
@@ -7,6 +7,7 @@
 
 namespace yiiunit\framework\i18n;
 
+use Yii;
 use yii\base\Event;
 use yii\i18n\I18N;
 use yii\i18n\PhpMessageSource;
@@ -35,13 +36,19 @@ class I18NTest extends TestCase
     {
         $this->i18n = new I18N([
             'translations' => [
-                'test' => new PhpMessageSource([
+                'test' => [
+                    'class' => $this->getMessageSourceClass(),
                     'basePath' => '@yiiunit/data/i18n/messages',
-                ])
+                ]
             ]
         ]);
     }
 
+    private function getMessageSourceClass()
+    {
+        return PhpMessageSource::className();
+    }
+
     public function testTranslate()
     {
         $msg = 'The dog runs fast.';
@@ -63,13 +70,14 @@ class I18NTest extends TestCase
     {
         $i18n = new I18N([
             'translations' => [
-                '*' => new PhpMessageSource([
+                '*' => [
+                    'class' => $this->getMessageSourceClass(),
                     'basePath' => '@yiiunit/data/i18n/messages',
                     'fileMap' => [
                         'test' => 'test.php',
                         'foo' => 'test.php',
                     ],
-                ])
+                ]
             ]
         ]);
 
@@ -174,15 +182,15 @@ class I18NTest extends TestCase
 
     public function testUsingSourceLanguageForMissingTranslation()
     {
-        \Yii::$app->sourceLanguage = 'ru';
-        \Yii::$app->language = 'en';
+        Yii::$app->sourceLanguage = 'ru';
+        Yii::$app->language = 'en';
 
         $msg = '{n, plural, =0{Нет комментариев} =1{# комментарий} one{# комментарий} few{# комментария} many{# комментариев} other{# комментария}}';
-        $this->assertEquals('5 комментариев', \Yii::t('app', $msg, ['n' => 5]));
-        $this->assertEquals('3 комментария', \Yii::t('app', $msg, ['n' => 3]));
-        $this->assertEquals('1 комментарий', \Yii::t('app', $msg, ['n' => 1]));
-        $this->assertEquals('21 комментарий', \Yii::t('app', $msg, ['n' => 21]));
-        $this->assertEquals('Нет комментариев', \Yii::t('app', $msg, ['n' => 0]));
+        $this->assertEquals('5 комментариев', Yii::t('app', $msg, ['n' => 5]));
+        $this->assertEquals('3 комментария', Yii::t('app', $msg, ['n' => 3]));
+        $this->assertEquals('1 комментарий', Yii::t('app', $msg, ['n' => 1]));
+        $this->assertEquals('21 комментарий', Yii::t('app', $msg, ['n' => 21]));
+        $this->assertEquals('Нет комментариев', Yii::t('app', $msg, ['n' => 0]));
     }
 
     /**
@@ -213,6 +221,50 @@ class I18NTest extends TestCase
         Event::off(PhpMessageSource::className(), PhpMessageSource::EVENT_MISSING_TRANSLATION);
     }
 
+    public function sourceLanguageDataProvider()
+    {
+        return [
+            ['en-GB'],
+            ['en']
+        ];
+    }
+
+    /**
+     * @dataProvider sourceLanguageDataProvider
+     * @param $sourceLanguage
+     */
+    public function testIssue11429($sourceLanguage)
+    {
+        $this->mockApplication();
+        $this->setI18N();
+
+        Yii::$app->sourceLanguage = $sourceLanguage;
+        $logger = Yii::getLogger();
+        $logger->messages = [];
+        $filter = function ($array) {
+            // Ensures that error message is related to PhpMessageSource
+            $className = $this->getMessageSourceClass();
+            return substr_compare($array[2], $className, 0, strlen($className)) === 0;
+        };
+
+        $this->assertEquals('The dog runs fast.', $this->i18n->translate('test', 'The dog runs fast.', [], 'en-GB'));
+        $this->assertEquals([], array_filter($logger->messages, $filter));
+
+        $this->assertEquals('The dog runs fast.', $this->i18n->translate('test', 'The dog runs fast.', [], 'en'));
+        $this->assertEquals([], array_filter($logger->messages, $filter));
+
+        $this->assertEquals('The dog runs fast.', $this->i18n->translate('test', 'The dog runs fast.', [], 'en-CA'));
+        $this->assertEquals([], array_filter($logger->messages, $filter));
+
+        $this->assertEquals('The dog runs fast.', $this->i18n->translate('test', 'The dog runs fast.', [], 'hz-HZ'));
+        $this->assertCount(1, array_filter($logger->messages, $filter));
+        $logger->messages = [];
+
+        $this->assertEquals('The dog runs fast.', $this->i18n->translate('test', 'The dog runs fast.', [], 'hz'));
+        $this->assertCount(1, array_filter($logger->messages, $filter));
+        $logger->messages = [];
+    }
+
     /**
      * Formatting a message that contains params but they are not provided.
      * https://github.com/yiisoft/yii2/issues/10884