diff --git a/classes/migration/upgrade/v3_4_0/MergeLocalesMigration.php b/classes/migration/upgrade/v3_4_0/MergeLocalesMigration.php
new file mode 100644
index 00000000000..70182c852d1
--- /dev/null
+++ b/classes/migration/upgrade/v3_4_0/MergeLocalesMigration.php
@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file classes/migration/upgrade/v3_4_0/MergeLocalesMigration.php
+ *
+ * Copyright (c) 2014-2021 Simon Fraser University
+ * Copyright (c) 2000-2021 John Willinsky
+ * Distributed under the GNU GPL v3. For full terms see the file docs/COPYING.
+ *
+ * @class MergeLocalesMigration
+ *
+ * @brief Change Locales from locale_countryCode localization folder notation to locale localization folder notation
+ */
+
+namespace APP\migration\upgrade\v3_4_0;
+
+use Illuminate\Support\Collection;
+
+class MergeLocalesMigration extends \PKP\migration\upgrade\v3_4_0\MergeLocalesMigration
+{
+    protected string $CONTEXT_TABLE = 'presses';
+    protected string $CONTEXT_SETTINGS_TABLE = 'press_settings';
+    protected string $CONTEXT_COLUMN = 'press_id';
+
+    protected function getSettingsTables(): Collection
+    {
+        return collect([
+            'press_settings' => 'press_id',
+            'publication_format_settings' => 'publication_format_id',
+            'series_settings' => 'series_id',
+            'spotlight_settings' => 'spotlight_id',
+            'submission_chapter_settings' => 'chapter_id',
+        ])->merge(parent::getSettingsTables());
+    }
+}
diff --git a/config.TEMPLATE.inc.php b/config.TEMPLATE.inc.php
index 8ef7fdf000a..a04b1d510fd 100644
--- a/config.TEMPLATE.inc.php
+++ b/config.TEMPLATE.inc.php
@@ -196,7 +196,7 @@
 [i18n]
 
 ; Default locale
-locale = en_US
+locale = en
 
 ; Database connection character set
 connection_charset = utf8
diff --git a/dbscripts/xml/upgrade.xml b/dbscripts/xml/upgrade.xml
index bf02577b184..ecd980afdc8 100644
--- a/dbscripts/xml/upgrade.xml
+++ b/dbscripts/xml/upgrade.xml
@@ -168,6 +168,7 @@
 		<migration class="APP\migration\upgrade\v3_4_0\I7128_SeriesEntityDAORefactor" />
 		<migration class="PKP\migration\upgrade\v3_4_0\I7486_RenameUnconsideredColumnToConsidered"/>
 		<migration class="PKP\migration\upgrade\v3_4_0\I7486_RemoveItemViewsTable"/>
+		<migration class="APP\migration\upgrade\v3_4_0\MergeLocalesMigration"/>
 		<data file="dbscripts/xml/upgrade/3.4.0_preupdate_email_templates.xml" />
 		<note file="docs/release-notes/README-3.4.0" />
 	</upgrade>