Filter PayPal-supported language codes

modules/ppcp-api-client/src/Repository/class-applicationcontextrepository.php

@@ -46,7 +46,7 @@ public function current_context(
 	): ApplicationContext {
 
 		$brand_name  = $this->settings->has( 'brand_name' ) ? $this->settings->get( 'brand_name' ) : '';
-		$locale      = str_replace( '_', '-', get_user_locale() );
+		$locale      = $this->valid_bcp47_code();
 		$landingpage = $this->settings->has( 'landing_page' ) ?
 			$this->settings->get( 'landing_page' ) : ApplicationContext::LANDING_PAGE_NO_PREFERENCE;
 		$context     = new ApplicationContext(
@@ -59,4 +59,24 @@ public function current_context(
 		);
 		return $context;
 	}
+
+	/**
+	 * Returns a PayPal-supported BCP-47 code, for example de-DE-formal becomes de-DE.
+	 *
+	 * @return string
+	 */
+	protected function valid_bcp47_code() {
+		$locale = str_replace( '_', '-', get_user_locale() );
+
+		if ( preg_match( '/^[a-z]{2}(?:-[A-Z][a-z]{3})?(?:-(?:[A-Z]{2}))?$/', $locale ) ) {
+			return $locale;
+		}
+
+		$parts = explode( '-', $locale );
+		if ( count( $parts ) === 3 ) {
+			return substr( $locale, 0, strrpos( $locale, '-' ) );
+		}
+
+		return 'en';
+	}
 }

modules/ppcp-button/src/Assets/class-smartbutton.php

@@ -726,7 +726,6 @@ private function url(): string {
 		$params = array(
 			'client-id'        => $this->client_id,
 			'currency'         => get_woocommerce_currency(),
-			'locale'           => get_user_locale(),
 			'integration-date' => PAYPAL_INTEGRATION_DATE,
 			'components'       => implode( ',', $this->components() ),
 			'vault'            => $this->can_save_vault_token() ?

tests/PHPUnit/ApiClient/Repository/ApplicationContextRepositoryTest.php

@@ -0,0 +1,38 @@
+<?php
+declare(strict_types=1);
+
+namespace WooCommerce\PayPalCommerce\ApiClient\Repository;
+
+use WooCommerce\PayPalCommerce\ApiClient\TestCase;
+use WooCommerce\PayPalCommerce\Button\Assets\SmartButton;
+use function Brain\Monkey\Functions\when;
+
+class ApplicationContextRepositoryTest extends TestCase
+{
+    /**
+     * @dataProvider provider
+     */
+    public function test_valid_bcp47_code($input, $output)
+    {
+        $testee = $this->getMockBuilder(ApplicationContextRepository::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $method = new \ReflectionMethod($testee, 'valid_bcp47_code');
+        $method->setAccessible(true);
+
+        when('get_user_locale')->justReturn($input);
+
+        $this->assertSame($output, $method->invoke($testee));
+    }
+
+    public function provider()
+    {
+        return [
+            'de-DE' => ['de-DE', 'de-DE'],
+            'de-DE-formal' => ['de-DE-formal', 'de-DE'],
+            'de' => ['de', 'de'],
+            'ceb' => ['ceb', 'en'],
+        ];
+    }
+}