diff --git a/classes/cliTool/InstallTool.php b/classes/cliTool/InstallTool.php
index 216b50033ff..5f6d7ac908f 100644
--- a/classes/cliTool/InstallTool.php
+++ b/classes/cliTool/InstallTool.php
@@ -84,7 +84,7 @@ public function readParams()
 
         // Locale Settings
         $this->printTitle('installer.localeSettings');
-        $this->readParamOptions('locale', 'locale.primary', $installForm->supportedLocales, 'en_US');
+        $this->readParamOptions('locale', 'locale.primary', $installForm->supportedLocales, 'en');
         $this->readParamOptions('additionalLocales', 'installer.additionalLocales', $installForm->supportedLocales, '', true);
 
         // File Settings
diff --git a/classes/i18n/interfaces/LocaleInterface.php b/classes/i18n/interfaces/LocaleInterface.php
index 1459ac18772..257f466608a 100644
--- a/classes/i18n/interfaces/LocaleInterface.php
+++ b/classes/i18n/interfaces/LocaleInterface.php
@@ -32,7 +32,7 @@
 interface LocaleInterface extends \Illuminate\Contracts\Translation\Translator
 {
     /** Keeps the default locale of the application */
-    public const DEFAULT_LOCALE = 'en_US';
+    public const DEFAULT_LOCALE = 'en';
 
     /** Regular expression to validate and extract pieces of a locale, variants can be composed of five to eight letters, or of four characters starting with a digit */
     public const LOCALE_EXPRESSION = '/^(?P<language>[a-z]{2})(?:_(?P<country>[A-Z]{2}))?(?:@(?P<script>[A-Za-z\d]{5,8}|\d[A-Za-z\d]{3}))?$/';
diff --git a/classes/install/Installer.php b/classes/install/Installer.php
index 0daf0f55904..311726367de 100644
--- a/classes/install/Installer.php
+++ b/classes/install/Installer.php
@@ -52,7 +52,7 @@ class Installer
     public const INSTALLER_ERROR_DB = 2;
 
     public const INSTALLER_DATA_DIR = 'dbscripts/xml';
-    public const INSTALLER_DEFAULT_LOCALE = 'en_US';
+    public const INSTALLER_DEFAULT_LOCALE = 'en';
 
     /** @var string descriptor path (relative to INSTALLER_DATA_DIR) */
     public $descriptor;
diff --git a/classes/migration/install/CommonMigration.php b/classes/migration/install/CommonMigration.php
index 41c07d47e09..ba94e390f6b 100644
--- a/classes/migration/install/CommonMigration.php
+++ b/classes/migration/install/CommonMigration.php
@@ -45,7 +45,7 @@ public function up(): void
             $table->bigInteger('redirect')->default(0)->comment('If not 0, redirect to the specified journal/conference/... site.');
             $table->string('primary_locale', 14)->comment('Primary locale for the site.');
             $table->smallInteger('min_password_length')->default(6);
-            $table->string('installed_locales', 1024)->default('en_US')->comment('Locales for which support has been installed.');
+            $table->string('installed_locales', 1024)->default('en')->comment('Locales for which support has been installed.');
             $table->string('supported_locales', 1024)->comment('Locales supported by the site (for hosted journals/conferences/...).')->nullable();
             $table->string('original_style_file_name', 255)->nullable();
         });
@@ -196,7 +196,7 @@ public function up(): void
         // Default data for email templates.
         Schema::create('email_templates_default_data', function (Blueprint $table) {
             $table->string('email_key', 255)->comment('Unique identifier for this email.');
-            $table->string('locale', 14)->default('en_US');
+            $table->string('locale', 14)->default('en');
             $table->string('name', 255);
             $table->string('subject', 255);
             $table->text('body')->nullable();
diff --git a/tests/config/config.TEMPLATE.mysql.inc.php b/tests/config/config.TEMPLATE.mysql.inc.php
index cbcd528675a..6b1a003a4ec 100644
--- a/tests/config/config.TEMPLATE.mysql.inc.php
+++ b/tests/config/config.TEMPLATE.mysql.inc.php
@@ -34,7 +34,7 @@
 web_cache_hours = 1
 
 [i18n]
-locale = en_US
+locale = en
 connection_charset = utf8
 
 [files]
diff --git a/tools/buildSwagger.php b/tools/buildSwagger.php
index d90c12a392b..66d9dd84a63 100644
--- a/tools/buildSwagger.php
+++ b/tools/buildSwagger.php
@@ -65,7 +65,7 @@ public function execute()
                 exit;
             }
 
-            $locales = ['en_US', 'fr_CA'];
+            $locales = ['en', 'fr_CA'];
 
             $apiSchema = json_decode($source);
             foreach ($apiSchema->definitions as $definitionName => $definition) {
diff --git a/xml/schema/common.xml b/xml/schema/common.xml
index 2f32631317d..ea6e8d080ca 100644
--- a/xml/schema/common.xml
+++ b/xml/schema/common.xml
@@ -99,7 +99,7 @@
 		</field>
 		<field name="installed_locales" type="C2" size="1024">
 			<NOTNULL/>
-			<DEFAULT VALUE="en_US"/>
+			<DEFAULT VALUE="en"/>
 			<descr>Locales for which support has been installed.</descr>
 		</field>
 		<field name="supported_locales" type="C2" size="1024">
@@ -456,7 +456,7 @@
 		</field>
 		<field name="locale" type="C2" size="14">
 			<NOTNULL />
-			<DEFAULT VALUE="en_US"/>
+			<DEFAULT VALUE="en"/>
 		</field>
 		<field name="subject" type="C2" size="120">
 			<NOTNULL/>