Yoast giving error when choosing my language

Yoast is working fine when my language is English (us), but when I chance it to Finnish it give two errors:

Notice: Undefined offset: 1 in /wp-content/plugins/wordpress-seo/admin/class-admin-asset-manager.php on line 69

Notice: Undefined offset: 1 in /wp-content/plugins/wordpress-seo/admin/class-admin-asset-manager.php on line 69

Here is the code from class-admin-asset-manager.php on line 69:

/**
* Calls the functions that register scripts and styles with the scripts and styles to be registered as arguments.
*/
public function register_assets() {
$locale = get_locale();
list( $language, $territory ) = explode( ‘_’, $locale );

wp_register_script(
self::PREFIX . ‘intl-polyfill’,
sprintf( ‘https://cdn.polyfill.io/v2/polyfill.min.js?features=Intl.~locale.%s’, $language ),
array(),
WPSEO_VERSION
);

$this->register_scripts( $this->scripts_to_be_registered() );
$this->register_styles( $this->styles_to_be_registered() );
}

Any ideas how to fix this problem?
My Yoast version is 5.9.2
And WP versio 4.91