diff --git a/src/wp-includes/class.wp-scripts.php b/src/wp-includes/class.wp-scripts.php
index a629248df4..4d7bd9e1b2 100644
--- a/src/wp-includes/class.wp-scripts.php
+++ b/src/wp-includes/class.wp-scripts.php
@@ -484,12 +484,29 @@ class WP_Scripts extends WP_Dependencies {
 			unset( $l10n['l10n_print_after'] );
 		}
 
-		foreach ( (array) $l10n as $key => $value ) {
-			if ( ! is_scalar( $value ) ) {
-				continue;
-			}
+		if ( ! is_array( $l10n ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				sprintf(
+					/* translators: 1: $l10n, 2: wp_add_inline_script() */
+					__( 'The %1$s parameter must be an array. To pass arbitrary data to scripts, use the %2$s function instead.' ),
+					'<code>$l10n</code>',
+					'<code>wp_add_inline_script()</code>'
+				),
+				'5.7.0'
+			);
+		}
 
-			$l10n[ $key ] = html_entity_decode( (string) $value, ENT_QUOTES, 'UTF-8' );
+		if ( is_string( $l10n ) ) {
+			$l10n = html_entity_decode( $l10n, ENT_QUOTES, 'UTF-8' );
+		} else {
+			foreach ( (array) $l10n as $key => $value ) {
+				if ( ! is_scalar( $value ) ) {
+					continue;
+				}
+
+				$l10n[ $key ] = html_entity_decode( (string) $value, ENT_QUOTES, 'UTF-8' );
+			}
 		}
 
 		$script = "var $object_name = " . wp_json_encode( $l10n ) . ';';
diff --git a/tests/phpunit/tests/dependencies/scripts.php b/tests/phpunit/tests/dependencies/scripts.php
index cbe13a66df..838ac454d3 100644
--- a/tests/phpunit/tests/dependencies/scripts.php
+++ b/tests/phpunit/tests/dependencies/scripts.php
@@ -1428,4 +1428,67 @@ JS;
 			$this->assertSame( $found, 0, "sourceMappingURL found in $js_file" );
 		}
 	}
+
+	/**
+	 * @ticket 52534
+	 * @covers ::wp_localize_script
+	 *
+	 * @dataProvider data_wp_localize_script_data_formats
+	 *
+	 * @param mixed  $l10n_data Localization data passed to wp_localize_script().
+	 * @param string $expected  Expected transformation of localization data.
+	 * @param string $warning   Optional. Whether a PHP native warning/error is expected. Default false.
+	 */
+	public function test_wp_localize_script_data_formats( $l10n_data, $expected, $warning = false ) {
+		if ( $warning ) {
+			if ( PHP_VERSION_ID < 80000 ) {
+				$this->expectException( 'PHPUnit_Framework_Error_Warning' );
+			} else {
+				// As this exception will only be set on PHP 8 in combination with PHPUnit 7, this will work (for now).
+				$this->expectException( 'Error' );
+			}
+		}
+
+		if ( ! is_array( $l10n_data ) ) {
+			$this->setExpectedIncorrectUsage( 'WP_Scripts::localize' );
+		}
+
+		wp_enqueue_script( 'test-example', 'example.com', array(), null );
+		wp_localize_script( 'test-example', 'testExample', $l10n_data );
+
+		$expected  = "<script type='text/javascript' id='test-example-js-extra'>\n/* <![CDATA[ */\nvar testExample = {$expected};\n/* ]]> */\n</script>\n";
+		$expected .= "<script type='text/javascript' src='http://example.com' id='test-example-js'></script>\n";
+
+		$this->assertSame( $expected, get_echo( 'wp_print_scripts' ) );
+	}
+
+	/**
+	 * Data provider for test_wp_localize_script_data_formats().
+	 *
+	 * @return array[] {
+	 *     Array of arguments for test.
+	 *
+	 *     @type mixed  $l10n_data Localization data passed to wp_localize_script().
+	 *     @type string $expected  Expected transformation of localization data.
+	 *     @type string $warning   Optional. Whether a PHP native warning/error is expected.
+	 * }
+	 */
+	public function data_wp_localize_script_data_formats() {
+		return array(
+			// Officially supported formats.
+			array( array( 'array value, no key' ), '["array value, no key"]' ),
+			array( array( 'foo' => 'bar' ), '{"foo":"bar"}' ),
+			array( array( 'foo' => array( 'bar' => 'foobar' ) ), '{"foo":{"bar":"foobar"}}' ),
+			array( array( 'foo' => 6.6 ), '{"foo":"6.6"}' ),
+			array( array( 'foo' => 6 ), '{"foo":"6"}' ),
+
+			// Unofficially supported format.
+			array( 'string', '"string"' ),
+
+			// Unsupported formats.
+			array( 1.5, '1.5', true ),
+			array( 1, '1', true ),
+			array( false, '[""]' ),
+		);
+	}
 }